-NRLF 


C    E    fl?0 


GIFT   OF 


THE   TRANSMISSION   OF  NERVOUS  IMPULSES 

IN  RELATION  TO  LOCOMOTION 

IN  THE  EARTHWORM 


A  THESIS  SUBMITTED  IN  PARTIAL  SATISFACTION  OF 
THE  REQUIREMENTS  FOR  THE  DEGREE  OF 

DOCTOR  OF  PHILOSOPHY 
AT  THE  UNIVERSITY  OF  CALIFORNIA 


MAY,  1917 


The   Transmission   of  Nervous    Impulses 
in  Relation    to    Locomotion 
in   the  Earthworm 


John  P.   Bo vard 

A  thesis   presented   to    the   faculty  of   the 
College  of  Letters   and  Science 

in   the 

University  of  California 
in  partial  fulfillment  of  the  requirements 

for  the  degree  of 
Doctor  of  Philosophy. 


Approved  by  subcommittee  in  charge 


.  Chairman 


Berkeley,    California. 


UNIVERSITY    OF    CALIFORNIA    PUBLICATIONS 
IN 

ZOOLOGY 

Vol.  18,  No.  7,  pp.  103-134,  14  figures  in  text  January  7,  1918 


THE  TRANSMISSION  OF  NERVOUS  IMPULSES 

IN   RELATION   TO   LOCOMOTION 

IN  THE  EARTHWORM 


BY 

JOHN   F.  BOVARD 


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BERKELEY 


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UNIVERSITY    OF    CALIFORNIA    PUBLICATIONS 

IN 

ZOOLOGY 

Vol.  18,  No.  7,  pp.  103-134,  14  figures  in  text  January  7,  1918 


THE  TRANSMISSION  OF  NERVOUS  IMPULSES 

IN  RELATION  TO  LOCOMOTION 

IN  THE  EARTHWORM 


BY 

JOHN  F.  BOVAKD 


CONTENTS 

PAGE 

Introduction 104 

I.  Work  of  Friedliinder  104 

II.  Anesthesia  experiments  of  Krukenberg  105 

III.  Work  of  Biedermann  105 

Materials  and  methods  106 

I.  Materials    106 

II.  Methods 106 

1.  Biedermann 's  method  106 

2.  Anesthesia  method  by  ether  and  nitric  acid  107 

State  of  anesthetized  area  107 

The  problem  108 

Acknowledgments 108 

Experiments  with  anesthetized  worms  108 

I.  Free  moving  animals  109 

II.  The  tension  factor  109 

III.  Autotomy  : Ill 

IV.  Free  nerve  preparations  112 

1.  Dissection  experiments 113 

2.  Graphic  records  114 

3.  Effects  of  stovaine  116 

V.  Limits  of  transmission  118 

VI.  Dependence  on  the  nervous  system  for  transmission 120 

VII.  Eate  of  transmission  of  locomotor  impulses  122 

VIII.  Eate  of  transmission  of  giant  fiber  impulses 125 

Theoretical  considerations  128 

I.  Eeview  of  anatomy 129 

II.  Theory  of  reinforced  stimuli  131 

Summary 132 

Literature  cited  ..  ..  134 


-  •     .  " 

~    ^  -  *-    •* 

». 

- 


104  University  of  California  Publications  in  Zoology      [V<>L-  18 


INTRODUCTION 

The  normal  creeping  movements  of  the  earthworm  proceed  as  fol- 
lows. The  first  movement  is  a  contraction  of  the  circular  muscles  of 
the  first  few  segments.  This  causes  an  extension  of  the  anterior  end. 
The  chaetae  now  become  directed  backwards  and  take  hold  on  the 
substrate  while  the  longitudinal  muscles  begin  a  contraction  which 
draws  the  next  few  segments  forward.  The  circular  muscles  in  each 
segment  contract,  one  segment  after  another  beginning  at  the  anterior 
end  and  proceeding  posteriorly.  Immediately  following  the  circular 
muscle  action  the  longitudinal  muscles  contract  so  that  a  wave  of 
extension  followed  by  a  shortening  can  be  seen  to  traverse  the  whole 
animal.  After  the  first  wave  of  muscular  activity  is  well  started 
posteriorly  another  may  be  initiated  and  at  any  one  time  several  of 
these  contraction  waves  may  be  seen  in  a  normally  creeping  worm. 

Some  years  ago  Friedlander  (1894)  showed  that  in  the  normal 
creeping  of  an  earthworm  the  nervous  system  played  only  a  small  part. 
When  a  section  of  the  nerve  cord  containing  ten  to  twelve  ganglia  was 
removed,  the  movements  of  the  parts  of  the  worm  were  still  perfectly 
coordinated.  The  most  important  part  of  the  activity  was  the  ' '  pull ' ' 
which  the  contraction  of  each  segment  as  the  wave  progresses  gave  to 
the  succeeding  segments.  The  wave-like  motion  of  the  contractions 
proceeding  down  the  length  of  the  animal  was  due,  first,  to  the  pull 
of  segments  on  each  other,  and,  secondly,  to  the  sequence  of  reflex 
actions  of  the  nerves  in  each  segment,  which  are  such  that  the  longi- 
tudinal muscles  follow  the  contractions  of  the  circular  muscles.  This 
nervous  mechanism  is,  according  to  Friedlander,  concerned  with  each 
segment  alone,  and  there  is  no  passage  of  impulses  up  or  down  the 
cord.  No  attempt  was  made  by  him  to  analyze  the  matter  of  tension 
or  pull,  or  to  determine  whether  coordination  wrould  proceed  without 
this  factor. 

In  order  to  show  that  the  nervous  system  was  entirely  secondary, 
Friedlander  cut  a  worm  into  two  pieces  and  then  joined  these  two  with 
a  thread  The  creeping  movements  of  the  anterior  piece  gave  the 
necessary  pull  on  the  posterior  piece  through  the  thread,  and  the  two 
parts  crept  along  in  perfect  coordination.  In  certain  special  cases, 
when  the  nerve  cord  was  destroyed  for  a  short  distance  without  tran- 
section  of  the  body,  the  parts  anterior  and  posterior  to  the  cordless 
region  moved  together  with  perfect  coordination.  According  to  this 


1918]  Bovard:  Nervous  Impulses  in  the  Earthworm  105 

view,  then,  the  nerve  cord  is  supplementary  and  concerned  only  with 
those  short  reflex  paths  which  are  mediated  by  a  single  ganglion. 
Previous  to  the  year  in  which  Friedlander  published  his  analysis  of 
the  movements  of  earthworms,  Krukenberg  (1881)  showed,  in  some 
work  on  leeches,  that  the  middle  section  of  the  animal  could  be 
anesthetized  with  the  result  that  the  parts  anterior  and  posterior  to 
this  region  still  acted  in  perfect  coordination.  In  these  animals,  how- 
ever, the  nervous  system  differs  structurally  from  that  of  an  oligo- 
chaete.  In  leeches  the  nerves  run  from  the  anterior  to  the  posterior  end, 
while  in  the  oligochaetes  the  only  long  nerves  are  the  giant  fibers,  the 
other  fibers  in  the  cord  being  those  of  short  neurones  extending  at 
most  from  one  ganglion  to  the  next.  The  anesthesia  in  leeches  affects 
only  the  peripheral  nerve  endings,  while  the  trunks  connecting  anterior 
and  posterior  portions  are  not  affected. 

The  more  recent  work  of  Biedermann  (1904)  becomes  particularly 
interesting,  however,  as  it  gives  some  new  light  on  the  function  of  the 
nerve  cord  of  the  earthworm.  In  this  work  on  the  comparative  physi- 
ology of  peristaltic  movements  he  compares  the  locomotor  action  in 
earthworms  to  the  rhythmic  movements  found  in  smooth  muscle. 
Biedermann  discovered  that  if  worms  were  placed  in  seven  per  cent 
alcohol  for  a  few  minutes  until  they  became  motionless  and  then  the 
middle  region  of  several  segments  was  anesthetized  with  nitric  acid  or 
pure  chloroform  for  a  few  seconds,  the  muscular  activity  of  the  sec- 
tion was  destroyed  and  all  response  to  stimulus  failed.  He  then  had  a 
worm  with  active  anterior  and  posterior  parts  connected  through  the 
anesthetized  area  by  a  nerve  cord.  In  creeping  movements,  the 
anesthetized  area,  or  dead  area,  acted  as  one  piece.  It  transmitted 
no  rhythmic  movements,  while  the  posterior  part  still  acted  in  perfect 
coordination  with  the  anterior  part. 

In  further  tests  by  Biedermann  of  the  transmission  of  impulses 
through  the  cord  over  more  than  one  segment,  he  pinned  such  anes- 
thetized specimens  to  a  cork  plate  by  needles  through  the  dead  mus- 
cular area  and  found  that  the  posterior  part  still  moved  in  perfect 
coordination  with  the  anterior  part.  With  regard  to  the  limits  of  this 
transmission  through  the  cord,  and  the  speed  of  the  impulses,  it  is 
stated  in  his  paper  (1904,  p.  493)  that  the  transmission  often  runs 
2-3  centimeters  in  4-5  seconds. 

In  the  interpretation  of  these  experiments  Biedermann  accepts  the 
theory  proposed  by  Friedlander,  except  that  in  order  to  explain  the 
coordinated  movements  of  posterior  pieces  when  a  certain  part  was 


106  University  of  California  Publications  in  Zoology      [VOL.  18 

anesthetized,  it  is  necessary  to  assume  that  the  impulses  run  through 
the  cord  for  a  considerable  distance  rather  than  through  one  ganglion 
as  Friedlander  supposed. 


MATERIALS  AND  METHODS 

Materials. — Several  species  of  worm  were  used  for  these  experi- 
ments. The  large  garden  worm,  Helodrilus  caliginosa,  was  favorable 
material  owing  to  its  size.  The  small  dung  worm,  Allolobophora 
foetida,  was  also  very  convenient  material  because  of  the  ease  of 
obtaining  the  material  during  the  winter.  No  difference  was  observed 
in  the  reactions  in  these  worms.  Unless  specially  noted  the  experi- 
ments recorded  will  refer  to  the  larger  worm,  Helodrilus. 

Methods. — Biedermann's  (1904)  method  of  anesthetizing  a  cer- 
tain portion  of  a  worm  by  use  of  nitric  acid  or  chloroform,  as  described, 
had  the  effect  of  killing  any  peripheral  nerve  endings  present  in  the 
part  and  of  impairing  the  muscle  cells.  It  left  the  anterior  and  pos- 
terior portions  connected,  however,  by  a  functioning  nerve  cord,  still 
intact,  except  that  no  stimuli  applied  to  the  treated  epithelium  were 
effective  in  setting  up  reflexes. 

It  was  suspected  by  Biedermann  that  as  locomotion  took  place  the 
posterior  part  was  acting  in  coordination,  not  only  because  it  was 
connected  to  the  anterior,  as  Friedlander  might  have  supposed  from 
his  string  experiment,  but  that  there  was  some  real  nervous  influence 
transmitted  by  the  cord  in  the  inert  middle  section.  In  order  to  test 
this  point  fully,  he  pinned  the  middle  anesthetized  portion  to  a  cork 
plate  to  remove  the  factor  of  tension,  when  it  was  found  that  the 
posterior  portion  still  made  movements  coordinated  with  those  of  the 
anterior  piece.  This  established  beyond  a  doubt  that  transmission 
did  take  place  over  a  longer  section  of  the  cord  than  the  earlier  in- 
vestigators had  deemed  necessary  and  showed  the  more  important  part 
played  by  the  nervous  system. 

In  developing  a  method  of  anesthesia  to  test  farther  the  matter  of 
transmission,  it  seemed  to  me  desirable  to  find  some  means  of  blocking 
reflexes  in  the  middle  area,,  and  yet  it  was  also  quite  necessary  at  the 
same  time  to  leave  the  muscle  tissue  and  the  central  nerve  cord  intact, 
only  the  peripheral  nervous  system  being  eliminated.  The  method 
developed  was  quite  different  from  that  of  Biedermann.  The  worm 
was  placed  on  a  glass  plate  slightly  moistened  with  water,  so  that  it 
was  slippery.  A  small  four-drahm  homeopathic  vial  containing  some 


1918]  Bovard:  Nervous  Impulses  in  the  Earthworm  107 

cotton  soaked  with  ether,  was  then  turned  down  over  the  worm  so  that 
the  mouth  of  the  bottle  covered  the  middle  section  of  the  worm.  It 
was  possible  to  hold  this  in  place  over  the  squirming  worm  until  the 
middle  part  was  anesthetized.  Owing  to  the  slipperiness  of  the  plate, 
the  worm  could  get  no  hold  and  autotomy  was  very  rare.  When, 
however,  as  occurred  in  early  experiments,  this  method  was  tried  on  a 
cork  plate,  autotomy  of  the  anterior  or  posterior  part  was  frequent 
because  of  the  hold  the  chaetae  were  able  to  take  on  the  cork  and  so 
the  worm  could  pull  itself  in  two.  Exposure  of  two  minutes  to  ether 
fumes  was  sufficient  for  complete  anesthesia,  but  had  little  effect  on 
the  muscle  tissue  itself.  The  worms  usually  recovered  completely  from 
the  effects  of  the  treatment  in  from  ten  minutes  to  an  hour.  During 
this  time  a  stimulus  to  the  muscle  in  the  anesthetized  area  called  forth 
a  direct  response  but  started  no  reactions  in  the  untreated  parts  of 
the  worm. 

In  using  some  of  the  larger  worms  this  simple  method  was  varied 
by  treating  the  etherized  area  with  six  per  cent  nitric  acid  for  ten 
seconds,  then  washing  the  whole  worm  in  water;  this  made  certain 
that  the  sensory  nerve  endings,  of  this  part,  were  rendered  functionless. 
In  cases  where  nitric  aid  was  used  the  worm  never  recovered  from  the 
treatment,  and  in  a  few  cases  where  the  worms  were  kept  for  a  few 
days  they  autotomized  the  posterior  and  middle  sections.  This  method 
was  used  where  only  a  nerve  bridge  was  desired  between  the  active 
anterior  and  posterior  parts,  as  in  measuring  the  speed  of  transmission 
of  impulses  in  the  nerve  cord. 

STATE  OF  THE  ANESTHETIZED  AREA 

For  a  very  short  period  after  treatment,  the  anesthetized  section 
looks  whitish  and  gives  off  a  great  deal  of  mucous,  but  later  the  appear- 
ance is  much  the  same  as  that  of  the  rest  of  the  worm,  except  for  an 
increase  in  diameter.  As  the  worm  begins  active  movement,  this 
middle  piece  decreases  in  diameter,  due  to  stretching,  for  it  acts  much 
like  a  rubber  band,  extending  and  then  contracting  with  each  creeping 
movement.  However,  no  waves  of  muscular  contraction  run  along 
its  length,  as  in  the  anterior  and  in  the  posterior  parts,  or  from  the 
former  to  the  latter. 

Stimulation  of  a  quiescent  worm  in  the  anesthetized  and  live 
regions  respectively  gives  a  marked  difference  in  response.  If  the 
anterior  part  is  touched  lightly  the  response  is  an  increase  in  diameter 
due  to  a  reflex  stimulation  of  the  longitudinal  muscles,  but  a  stimu- 


108  University  of  California  Publications  in  Zoology      [VOL.  18 

lation  of  the  middle  area  results  in  a  constriction,  due  to  the  contrac- 
tion of  the  circular  muscles  with  no  reflex  to  the  longitudinal  muscles. 
In  recovery  from  the  ether  treatment  the  longitudinal  muscles  recover 
and  reassume  normal  functions  first  and  the  circular  some  minutes 
later.  In  creeping  movements  the  middle  section  shows  that  the 
longitudinal  muscles  recover  their  nervous  connection  first,  for  they 
begin  to  contract  in  coordination  with  the  anterior  part,  some  time 
before  the  circular  muscles  begin  any  active  participation  in  the 
general  movement.  This  condition  is  due  no  doubt  to  the  fact  that 
the  longitudinal  muscles  lie  deeper  than  the  circulars  and  so  are  less 
affected  by  the  anesthesia.  In  addition  to  this  the  position  of  the 
longitudinal  muscle  is  closer  to  the  general  blood  supply,  which  would 
be  advantageous  in  the  removal  of  waste  products  and  the  bringing 
in  of  new  materials. 

THE  PROBLEM 

The  problem  then  suggests  itself :  how  is  this  transmission  through 
a  number  of  segments  accomplished?  (1)  Does  Biedermann's  dis- 
covery necessitate  the  existence  of  long  fiber  tracts  in  the  cord?  or, 
(2)  Can  it  be  explained  on  present  knowledge  of  the  neurones?  (3) 
Are  there  any  limits  to  the  transmission  through  anesthetized  areas? 
(4)  Can  the  speed  of  such  impulses  be  measured,  and  how  do  they 
compare  with  the  speed  of  nerve  impulses  in  other  annelids? 

ACKNOWLEDGMENTS 

The  greater  part  of  the  experimental  work  was  done  at  Harvard 
University  during  the  year  1914-1915,  under  the  general  direction 
of  Dr.  G.  H.  Parker,  to  whom  I  am  greatly  indebted  for  his  very 
kindly  interest  and  his  many  suggestions.  Later  the  work  of  bringing 
together  the  results  of  the  experimentation  was  done  at  the  University 
of  California.  I  wish  to  acknowledge  and  express  my  appreciation 
for  the  helpful  criticism  and  advice  of  Dr.  S.  S.  Maxwell,  of  the 
Department  of  Physiology,  and  to  Dr.  C.  A.  Kofoid,  of  the  Depart- 
ment of  Zoology,  for  the  general  supervision  of  the  work  and  the 
revision  of  this  paper. 

EXPERIMENTS  WITH  ETHERIZED  WORMS 
Problem. — Will  it  be  possible  to  get  transmission  of   locomotor 
impulses  through  an  anesthetized  area  in  both  directions,  from  anterior 
to  posterior  and  also  from  posterior  to  anterior  ? 


1918]  Bovard:  Nervous  Impulses  in  the  Earthworm  109 

Discussion. — If  a  worm  is  etherized  by  the  vial  method  and  allowed 
to  creep  on  a  damp  surface,  such  as  moist  filter  paper,  it  will  be  seen 
to  act  like  a  normal  worm  in  every  way,  except  that  the  middle  or 
etherized  portion  takes  no  part  in  the  contractions.  "With  each  pull 
of  the  anterior  piece  it  will  stretch  and  passively  contract  as  the  pos- 
terior piece  moves  up,  without  showing  the  normal  waves  of  muscular 
contraction  seen  in  the  active  portions. 

A  worm,  that  is  moving  anteriorly,  will  reverse  its  direction  and 
creep  posteriorly  if  stimulated  on  the  anterior  end.  Stimulation  of  the 
posterior  end  reverses  the  direction  again.  This  indicates  that  nerve 
impulses  may  pass  up  or  down  the  nerve  cord  and  that  these  impulses 
may  change  the  direction  of  the  creeping  movement,  but  it  does  not 
indicate  that  the  impulses  responsible  for  the  actual  creeping  pass 
through  the  nerve  bridge.  There  is  still  the  fact  that  the  muscles  in 
the  etherized  section  attaching  the  anterior  to  the  posterior  part  may 
act  as  the  "string"  in  Friedlander's  experiment  and  give  the  neces- 
sary pull  which  keeps  the  two  parts  working  in  coordination. 

Conclusion. — These  simple  experiments  only  show  that  there  may 
be  transmission  of  locomotor  impulses  in  both  directions  through  the 
nerve  cord  in  an  anesthetized  region  of  the  worm. 


TENSION 
(a)   Experiments  with  Etherized  Worms 

Problem. — To  what  extent  is  the  factor  of  tension  or  pull  respon- 
sible for  normal  locomotor  reactions? 

Method. — By  the  use  of  ether  in  anesthesia  we  are  able  to  test  out 
the  importance  of  the  matter  of  tension  or  pull  in  the  transmission  of 
locomotor  impulses.  It  will  be  remembered  that  the  etherized  part 
acts  as  one  piece.  No  waves  of  contraction  pass  up  or  down  this  part. 
A  small  piece  of  cork  was  glued  to  a  glass  plate  and  the  glass  plate 
kept  wet.  A  worm  prepared  by  etherizing  ten  segments  in  the  middle 
portion  was  pinned  to  the  cork  so  that  the  anterior  and  posterior  parts 
were  free  to  move,  but  the  middle  part  was  fixed. 

Discussion. — Under  these  conditions  no  movements  of  the  anterior 
part  could  exert  any  pull  on  the  posterior  piece.  In  all  such  experi- 
ments the  worms  behaved  as  Biedermann  (1904)  reported,  the  pos- 
terior piece  responding  with  locomotor  reactions  in  perfect  coordina- 
tion to  all  attempts  of  the  anterior  piece  to  make  creeping  movements. 
These  movements  could  not  be  accomplished  because  of  the  slippery 


110  University  of  California  Publications  in  Zoology      [VOL.  18 

glass  surface  and  the  pinning  down  of  the  middle  section,  but  the 
wave  of  contraction,  as  in  normal  creeping,  can  be  easily  observed 
(%.  1). 


ABC 

Fig.  1.  This  shows  the  method  of  pinning  the  anesthetized  region  of  the 
worm.  Kegion  A  has  just  made  an  anterior  creeping  movement  and  region  C 
can  be  seen  making  a  coordinated  movement.  On  account  of  being  pinned 
through  region  B,  the  anterior  part  of  C  is  forced  to  buckle. 

The  reversal  of  the  direction  of  these  movements  is  also  possible. 
Stimulation  of  the  anterior  end  will  cause  the  posterior  end  to  attempt 
creeping  posteriorly  with  the  anterior  piece  acting  in  perfect 
coordination. 

If,  now,  the  nerve  cord  be  severed  in  the  middle  region  without  dis- 
turbing the  muscular  connections  a  great  deal,  the  coordinated  move- 
ments of  the  two  ends  cease  and  become  independent  each  of  the 
other.  It  is  possible  when  a  worm  is  pinned  and  the  continuity  of 
nerve  in  the  anesthetized  area  is  broken,  that  the  anterior  and  pos- 
terior ends  may  each  be  making  locomotor  movements  in  opposite 
directions,  showing  an  independence  of  action  even  though  joined  by 
a  muscular  connection.  There  can  be,  therefore,  no  doubt  that  the 
nerve  cord  carries,  for  some  distance,  impulses  which  are  responsible 
for  locomotor  movements.  By  pinning  the  worm  to  the  cork,  the 
matter  of  tension  has  been  eliminated  and  by  cutting  the  nerve,  the 
transmission  through  the  nerve  cord  has  been  removed  and  coordinated 
movements  cease  entirely. 

AVhen  such  a  worm  with  transected  nerve  cord  and  anesthetized 
middle  section  is  released  from  its  cork  plate  and  allowed  to  creep 
freely,  it  is  found  that  the  coordination  of  anterior  and  posterior  parts 
is  perfect.  In  this  case,  however,  there  is  an  entirely  different 
explanation.  The  coordination  of  the  posterior  end  can  not  be  due  to 
any  nerve  impulses  from  the  anterior  end,  but  each  forward  move- 
ment of  the  anterior  section  causes  a  pull  on  the  posterior  piece  and 
this  starts  a  chain  of  reflexes  at  the  anterior  end  of  the  posterior  piece 
which  run  the  length  of  this  part  of  the  worm  and  give  rise  to  the 
muscular  contractions  which  normally  would  give  rise  to  locomotion. 


1918] 


Bovard:  Nervous  Impulses  in  the  Earthworm 


111 


In  worms  in  which  the  entire  dorsal  wall,  the  lateral  muscles,  and 
the  intestine  of  the  etherized  part  were  dissected  away  and  the  nerve 
cord  freed  from  the  ventral  muscle  by  cutting  the  lateral  roots,  the 
coordination  continued  perfect  in  function  between  the  anterior  and 
posterior  portions.  It  was  observed  that  such  specimens,  in  creeping, 
did  not  move  with  the  middle  section  tense,  as  a  string  connecting  the 
two  parts,  but  that  often  the  posterior  part  moved  along  rapidly, 
causing  the  middle  part  to  buckle  so  that  under  these  circumstances 
no  pull  could  possibly  have  been  exerted  on  the  posterior  part.  When 
the  anterior  part  was  pinned  down,  the  posterior  piece  still  continued 
its  coordinated  movements  and  "telescoped"  anteriorly  into  other 
parts. 

Conclusion. — Tension  or  pull,  while  important  in  normal  creeping 
movements,  may  be  eliminated  and  the  locomotor  stimulus  will  still 
pass  on  down  the  nerve  cord  for  some  distance. 


(&)  Autotomy 

In  the  course  of  administering  the  anesthesia  to  the  middle  portion 
of  the  worms,  it  sometimes  followed  that  the  strong  contractions 
would  break  the  muscular  walls  of  the  body,  a  condition  of  incomplete 
autotomy.  If  the  animal  was  released  in  time  the  anterior  and  pos- 
terior ends  would  remain  connected  by  the  intestine  and  the  nerve 
cord  (fig.  2). 


arvh  posf 

Fig.  2.  This  shows  the  nervous  bridge  as  made  in  an  incompletely  auto- 
tomized  worm.  The  break  in  the  musculature  occurs  between  the  segments. 
The  intestine  (int.),  with  the  dorsal  and  ventral  blood  vessels  (d.bl.v.  and  v.bl.v) 
and  a  portion  of  the  ventral  nerve  cord  (n.)}  may  be  seen. 

Problem. — Is  the  nervous  bridge  made  by  incomplete  autotomy 
between  anterior  and  posterior  ends  of  the  worm  capable  of  trans- 
mitting locomotor  impulses  in  both  directions  as  in  the  etherized 
worms  ? 


112  University  of  California  Publications  in  Zoology      [VOL.  18 

Discussion. — Under  these  circumstances  the  reactions  of  the  par- 
tially autotomized  worms  are  the  same  as  in  etherized  ones;  creeping 
anteriorly  and  posteriorly  can  be  induced  by  stimulation.  If  the 
anterior  end  is  pinned,  the  posterior  part  will  still  act  in  coordination ; 
in  this  case  the  only  possible  way  for  the  transmission  to  take  place 
would  be  through  the  nerve  cord.  Microscopical  sections  of  such  cases 
as  these  showed  that  the  nerve  card  was  quite  normal  in  structure  and 
still  intact. 

Friedlander  (1894)  laid  such  stress  on  the  matter  of  tension,  the 
pull  of  one  part  on  the  next  succeeding  segment,  that  the  behavior  of 
the  worm  under  these  conditions  of  anesthesia  becomes  particularly 
important  as  bearing  on  the  correctness  and  completeness  of  his 
explanation  (fig.  3). 


Fig.  3.  An  illustration  of  Friedlander 's  experiment  which  shows  the  anterior 
and  posterior  parts  of  the  worm  tied  together  with  a  thread.  The  movement 
of  the  anterior  piece  pulls  on  the  anterior  end  of  the  posterior  piece  and  starts 
the  locomotor  reactions  which  are  coordinated  with  those  of  the  anterior  half. 

Conclusion. — In  cases  where  the  tension  is  eliminated  by  pinning 
the  worm  to  a  cork  on  glass,  the  posterior  part  can  be  seen  to  begin 
rhythmical  movements  of  contraction  coordinated  with  those  of  the 
anterior  part.  If  this  anesthetized  portion  is  composed  of  but  few 
segments,  then  the  coordination  is  most  perfect  and  the  beginning  of 
the  movement  of  the  posterior  section  follows  in  shorter  time  than 
when  this  portion  of  the  worm  includes  many  segments.  It  is  possible 
to  anesthetize  a  section  of  such  length  that  no  coordination  is  carried 
on  and  the  posterior  part  lies  entirely  inert.  In  Helodrilus  trans- 
mission of  impulses  was  effective  through  20  segments,  rarely  through 
28,  and  never  through  more  than  30  segments. 

NERVE  FREE  PREPARATIONS 

Problem. — The  fact  that  the  worms  perform  autotomy  and  that  the 
anterior  and  posterior  parts  are  then  connected  with  each  other  only 
by  a  simple  nerve  bridge  and  the  intestine,  suggested  the  possibility  of 
dissecting  away  all  the  connecting  muscle  between  the  anterior  and 
posterior  parts.  Could  the  nerve  cord  be  dissected  free  for  a  distance 
exposing  several  ganglia  and  could  locomotor  impulses  be  transmitted 
through  such  a  cord? 


1918]  Bovard:  Nervous  Impulses  in  the  Earthworm  113 

Methods. — (a)  Dissection.  All  the  muscle  in  the  anesthetized 
region  was  cut  away  after  the  worm  had  been  pinned  to  a  cork  plate. 
Owing  to  the  fragility  of  the  nerve,  it  was  easily  broken  and  in  cases 
where  it  was  not  broken  it  was  easily  impaired  by  stretching,  so  that 
particular  care  had  to  be  taken  with  the  preparations  made.  Here, 
as  in  the  experiments  discussed  above,  where  transmission  was  over  a 
few  segments,  the  coordination  \vas  good  and  as  the  nerve  bridge  was 
lengthened  the  coordination  was  less  complete  and  finally  failed.  Such 
an  operation  must  have  a  decided  "shock"  effect  on  the  animal  and 
it  does  not  behave  as  would  be  expected  under  more  normal  conditions, 
consequently  the  length  of  the  nerve  does  not  represent  the  limits  of 
transmission,  as  will  be  shown  in  some  experiments  to  be  discussed 
later. 

In  all  these  cases  it  was  necessary  to  keep  the  worm  pinned,  for  if 
allowed  free  creeping  the  anterior  part  would  move  more  rapidly  than 
the  posterior,  the  nerve  was  not  strong  enough  to  drag  the  weight  of 
the  posterior  part  and  so  the  nerve  was  promptly  broken. 

In  my  first  dissections  all  of  the  musculature  in  the  anesthetized 
region  was  removed,  so  that  the  nerve  cord  was  the  only  connection 
between  the  anterior  and  posterior  parts  of  the  worm.  Later  I  modified 
this  so  that  the  nerve  cord,  while  entirely  free  for  several  segments, 
was  not  allowed  to  touch  the  cork  plate  but  was  kept  in  its  own  body 
fluids  on  a  piece  of  muscle  (fig.  4).  All  the  muscle  on  the  dorsal  and 


ar\{.  \.r  n.  posf 

Fig.  4.  Type  of  dissection  used  in  nerve  free  preparations,  (n.)  nerve  cord 
with  lateral  roots  cut  (l.r.),  intestine  (int.)  and  blood  vessels  (d.bl.v.  and  v.&Z.v.) 
cut  away. 

lateral  walls  was  dissected  off.  The  intestine  was  removed.  This  left 
the  nerve  cord  attached  to  the  ventral  plate  of  muscle.  A  sharp  flat 
stylet  was  introduced  under  the  nerve  cord  and  all  the  lateral  roots 
severed.  A  transverse  cut  was  then  made  across  the  ventral  muscle 
so  that  no  muscular  connection  remained  between  the  two  parts  of  the 
worm.  "When  this  type  of  operation  was  used  much  more  uniform 


114 


University  of  California  Publications  in  Zoology      [VOL.  18 


results  were  obtained  than  where  the  nerve  was  allowed  to  come  in 
contact  with  the  cork  of  the  dissecting  tray.  Garrey  and  Moore  (1916) 
used  a  method  similar  to  the  earlier  method  that  I  used  with  the  same 
general  results. 

(&)  Graphic  Records.  Apparatus.  As  a  check  on  the  observations 
just  described,  it  became  desirable  to  find  some  way  in  which  to  make 
a  graphic  record  showing  the  part  the  nerve  cord  plays  in  the  trans- 
mission of  locomotor  impulses.  The  movements  of  the  anterior  and 
posterior  ends  of  the  worm,  while  the  middle  part  was  fixed  to  a  cork 
plate  glued  on  glass,  suggested  that  if  levers  were  attached  to  these 
moving  parts  a  record  could  be  obtained  on  a  kymograph.  It  was 
necessary  in  order  to  obtain  good  records  to  have  the  levers  as  light 
as  possible  and  to  have  them  move  with  very  little  friction.  This  was 
accomplished  by  making  the  levers  of  aluminum  wire,  number  22.  A 
desired  length  was  inserted  in  a  cube  of  cork.  Through  the  cork  a 
small  glass  capillary  tube  was  thrust  which  made  the  bearing  for  the 
axle  of  the  lever.  A  very  fine  needle  was  then  fitted  into  the  glass 
capillary  and  the  needle  stuck  into  a  firm  support.  This  sort  of  a 
bearing  allowed  the  lever  to  move  with  little  friction  and  also  was 


Fig.  5.  The  general  arrangement  of  the  apparatus  for  recording  movements 
of  the  anterior  and  posterior  parts  of  the  worms.  Method  used  at  Harvard, 
1914-1915. 

a.l. — Aluminum  wire  lever  connected  to  anterior  end  of  worm  by  hook  and 
thread;  c. — Cork  plate  glued  to  glass  for  pinning  the  middle  anesthetized  por- 
tion; c.c. — Cork  cubes  through  which  aluminum  wires  run;  g.pl. — Glass  plate  to 
which  a  little  water  was  added  to  allow  the  worm  to  slide  back  and  forth  when 
pinned;  p.l. — Aluminum  wire  lever  connected  to  posterior  end  of  worm  by  hook 
and  thread;  Icy. — Drum  of  kymograph  for  taking  tracings  on  smoked  paper; 
wt. — Counter  balance  weights. 


1918] 


Bovard:  Nervous  Impulses  in  the  Earthworm 


115 


advantageous  in  that  it  allowed  little  side  lash.  Various  forms  of 
levers  could  be  built  up  by  means  of  extra  cork  cubes  and  short  sections 
of  aluminum  wire,  as  in  figure  5,  a.l.  and  p.l. 

The  levers  had  to  be  weighted  slightly  so  that  the  worm  would  be 
kept  in  a  straight  line  on  the  glass  plate  or  else  the  curves  recorded 
would  be  exceedingly  irregular  (fig.  5). 

If  now  a  worm  is  prepared  with  the  middle  part  anesthetized  and 
arranged  to  record  movements,  the  movements  of  the  posterior  part 
should  show  a  perfect  coordination  with  those  of  the  anterior  part 
(fig.  6). 


ant. 


post. 


Fig.  6.  Experiment  143.  A  record  showing  perfect  coordination  between 
anterior  and  posterior  parts  with  a  middle  area  of  eight  segments  anesthetized 
and  musculature  cut  away.  The  upper  curve  represents  the  movements  of  the 
anterior  end  and  the  lower  that  of  the  posterior  end.  Transmission  of  impulses 
mediated  through  the  nerve  cord  only. 

The  method  of  preparation  of  the  middle  portion  varied.  In  some 
cases  the  worm  was  treated  with  ether  by  the  vial  method,  and  then 
triple-pinned  to  the  cork  plate.  In  other  cases,  in  addition,  the  dorsal 
musculature  was  cut  away,  the  intestine  removed,  exposing  the  nerve 
cord,  and  the  lateral  branches  of  the  nerve  cord  transected.  In  still 
other  cases  the  musculature  was  cut  in  the  middle  region  but  not 


116 


University  of  California  Publications  in  Zoology      [VOL.  18 


removed,  so  the  nerve  could  rest  on  its  own  body  fluids.  In  all  these 
cases  coordinated  movements  of  anterior  and  posterior  portions  were 
shown.  The  best  records  were  obtained  when  the  least  dissection  was 
used. 

The  clinching  argument,  however,  was  obtained  when  during  the 
course  of  such  experiments  the  nerve  cord  is  cut.  In  all  such  cases,  no 
matter  what  type  of  dissection  was  used,  non-coordinated  movements 
were  shown  when  the  cord  was  transected  (fig.  7) . 


ant. 


post. 


Tig.  7.  Experiment  143.  Explanation  of  the  curves  here  the  same  as  in 
figure  6.  The  nerve  cord  connection  between  anterior  and  posterior  has  been 
cut.  Notice  the  lack  of  coordination  between  the  movements  of  two  portions 
of  the  worm. 


(c)  Stovaine.  Should  any  doubts  still  remain  concerning  trans- 
mission of  impulses  for  locomotor  movements  over  long  sections  of  the 
nerve  cord,  the  action  of  stovaine  will  set  these  completely  at  rest.  If 
stovaine  be  injected  into  the  body  cavity  of  the  worm  it  acts  as  a  block 
to  the  nerve  cord  over  four  or  five  segments  and  allows  no  impulses  to 
pass  up  or  down  through  the  segments  containing  the  anesthetic.  The 
records  will  show  that  there  is  a  lack  of  coordination  and  suppression 
of  movements  of  the  posterior  end  while  the  drug  is  effective  (fig.  8), 


1918]  Rovard:  Nervous  Impulses  in  the  Earthworm 

24  J  250 


117 


post. 


time  in 
Vs  sec. 


ant. 


Numbers  refer  to  time  of  day  animals  were  tested. 
Arrow  indicates  stimulus  given  to  the  anterior  end. 

Fig.  8.  Experiment  190.  Stovaine  injected  into  middle  section  of  worm, 
four  segments  affected.  Lower  curve  registers  the  movements  of  anterior  end 
and  upper  curve  those  of  the  posterior  end.  At  2:41  P.M.  the  coordination 
between  anterior  and  posterior  parts  is  not  normal,  and  at  2:50  P.M.  the  giant 
fiber  action  is  lost.  Stimulation  at  the  arrow  fails  to  give  a  reaction  in  the 
posterior  part.  » 

A  represents  ordinary  locomotor  activities. 

B  represents  giant  fiber  action. 

but  as  soon  as  the  effects  begin  to  wear  off,  the  coordination  between 
the  two  parts  becomes  more  and  more  complete  until  finally  the 
anterior  and  posterior  parts  are  again  acting  in  perfect  rhythm  (fig.  9) . 

The  supposition  in  this  case  is  that  stovaine  acts  on  tissue  of  earth- 
worm as  it  does  in  the  vertebrates,  where  it  has  no  effect  on  muscle  or 
nerve  endings  but  acts  only  as  a  "block"  on  nerve  fibers.  The  effects 
of  the  drug  were  kept  localized  to  small  sections  while  anteriorly  and 
posteriorly  all  the  normal  reactions  could  be  obtained. 

Conclusion. — The  nerve-free  preparations,  the  graphic  records  of 
movements  before  and  after  the  nerve  was  cut,  and  the  physiological 
block  established  by  stovaine,  all  go  to  show  that  the  locomotor  impulses 
travel  considerable  distances  in  the  cord.  This  work  confirms  the 
results  obtained  by  Biedermann  but  by  quite  different  methods.  The 
most  important  aspect  of  these  results  is  the  demonstration  that 


118 


University  of  California  Publications  in  Zoology      [VOL.  18 


locomotor  impulses  are  not  "short  relays"  depending  on  a  stimulus 
from  each  segment,  but  are  capable  of  running  a  number  of  segments 
with  no  stimulus  from  the  outside. 


post. 


time  in 
Vs  sec. 


ant. 


A  B 

Fig.  9.  Experiment  190.  Continuation  of  experiment  shown  in  figure  8.  At 
6:20  P.M.  the  worm  had  recovered  from  the  effects  of  the  stovaine.  Normal 
coordinated  movements  are  being  made  (A)  and  the  giant  fiber  action  has 
returned  (-B).  Stimulation  of  the  anterior  end  at  the  arrow  shows  a  response 
in  the  posterior  end. 


LIMITS  OF  TRANSMISSION 

Problem. — How  far  will  these  locomotor  impulses  travel  in  the 
cord?  Can  a  middle  area  of  sufficient  length  be  anesthetized  so  that 
no  impulses  from  the  anterior  piece  can  get  through  to  start  locomotion 
in  the  posterior  part? 

Discussion. — It  was  soon  discovered  that  transmission  was  best 
shown  when  it  was  concerned  with  few  segments  and  that,  as  the 
number  of  ganglia  through  which  the  impulse  must  pass  was  increased, 
the  coordination  became  less  and  less  perfect.  No  sharp  limits  could 
be  determined.  When  the  nerve  cord  was  dissected  free  from  muscle, 
the  most  severe  type  of  dissection,  the  transmission  seemed  to  be 
limited  to  eight  free  ganglia.  In  one  case,  coordinated  movements 
were  obtained  when  ten  ganglia  had  been  freed,  but  this  was  unique. 


1918]  Bovard:  Nervous  Impulses  in  the  Earthworm  119 

When  the  length  of  the  free  nerve  contained  four  ganglia,  transmission 
was  easily  demonstrated. 

In  those  cases  where  the  dissection  included  the  removal  of  the 
dorsal  wall,  intestine,  and  the  transection  of  lateral  nerves,  the  trans- 
mission easily  ran  for  more  than  ten  segments,  but  never  for  more 
than  twenty-eight. 

It  has  been  demonstrated  by  Biedermann  (1904)  and  confirmed  by 
my  own  experiments,  that  the  impulses  run  long  distances  in  the  cord 
when  the  worms  are  anesthetized  in  the  middle  region  which  is  after- 
wards treated  with  six  per  cent  nitric  acid.  In  such  cases,  records  of 
transmission  were  obtained  when  twenty  segments  intervened  between 
the  still  active  anterior  and  posterior  ends.  Failures  came  more  often 
as  the  length  of  this  etherized  part  was  increased.  One  record  was 
obtained  with  the  large  Helodrilus  where  coordinationed  movements 
appeared  in  the  posterior  part  when  twenty-eight  segments  were 
etherized  and  their  muscles  killed  with  nitric  acid. 

These  results  fall  somewhat  short  of  the  cases  reported  by  Bieder- 
mann, where  coordinated  movements  were  obtained  through  anes- 
thetized parts  two  to  three  centimeters  long,  but  the  number  of  seg- 
ments is  not  stated.  The  greater  part  of  my  records  were  obtained  on 
Helodrilus,  where  twenty  segments  of  the  body,  in  the  part  measured, 
approximated  two  centimeters.  While  this  does  not  show  a  great  dis- 
crepancy, my  results  are  apparently  nearer  the  lower  figure  quoted  by 
Biedermann. 

We  can  establish,  then,  no  absolute  limits,  except  to  say  that  trans- 
mission is  fairly  well  accomplished  over  ten  segments,  may  run  to 
twenty  and  even  to  twenty-eight,  but  that  the  longer  the  nervous 
bridge  the  greater  the  difficulty.  No  records  have  been  obtained  where 
thirty  segments  were  concerned. 

One  factor  which  makes  the  determination  of  any  such  records 
very  difficult  is  that  impulses  from  normal  stimuli  in  normal  worms 
starting  down  the  length  of  the  worm  do  not  necessarily  continue  to 
the  end.  The  dying  out  of  an  impulse  is  quite  a  usual  phenomenon 
seen  in  the  contraction  waves  that  run  only  part  way  down  the  animal. 
One  of  these  impulses  may  start  into  the  cord  of  the  etherized  part 
and  never  reach  the  other  end  of  the  etherized  part  of  the  worm.  This 
does  not  mean  that  no  impulses  can  come  through,  and  so  no  limit  can 
be  determined  by  this  failure,  but  it  does  indicate  a  dying  out  of  this 
particular  impulse  somewhere  in  transit.  Therefore,  in  the  experi- 
mental determination  of  the  limits  to  transmission,  as  long  as  impulses 


120  University  of  California  Publications  in  Zoology      [VOL.  18 

come  through  the  etherized  part  we  are  still  within  the  limits  of  trans- 
mission, but  as  soon  as  failures  become  frequent  it  is  evident  that  the 
limits  have  been  approached.  More  refined  methods  may  be  able  to 
determine  these  limits  closely.  My  records  can  be  considered  only  as 
approximations. 

One  other  difficulty  arises  in  making  these  determinations.  Sum- 
mation of  stimuli  has  been  shown  by  both  Straub  (1900)  and  Buding- 
ton  (1902)  for  annelid  muscle.  Weak  stimuli  adding  themselves 
together  will  sooner  or  later  give  a  contraction.  There  is  the  possi- 
bility that,  in  observations  on  these  reactions,  failures  have  been 
recorded,  where,  in  reality,  weak  stimuli  did  get  through.  However, 
any  errors  so  made  would  be  on  the  conservative  side. 

Conclusions. — The  results  of  these  experiments  show  that  no 
absolute  limits  can  be  set,  the  impulses  travel  short  distances  in  the 
cord  very  readily  and  that  the  longer  the  section  of  cord  to  be  traversed 
the  greater  the  difficulty.  In  Helodrilus  twenty:eight  segments  was 
the  limit  for  the  distance  locomotor  impulses  would  travel  in  the  cord 
when  the  superficial  nerves  were  anesthetized. 

DEPENDENCE  ON  NERVOUS  SYSTEM  FOR  TRANSMISSION 

Problem. — While  the  nerve  cord  is  capable  of  transmitting  loco- 
motor  impulses  for  considerable  distances  is  it  possible  for  the  muscles 
to  carry  on  rhythmical  movements  without  the  aid  of  the  nervous 
system  ? 

Discussion. — If  a  short  section  of  a  worm  containing  about  twenty 
to  thirty  segments  is  prepared  in  such  a  way  that  it  will  give  a  record 
of  contractions  of  the  longitudinal  muscles  on  a  moving  drum,  and  the 
lever  is  slightly  weighted  so  the  piece  will  be  kept  straight  but  not 
stretched,  it  will  be  found  to  make  rhythmic  contractions.  Straub 
(1900)  and  Budington  (1902)  show  this  characteristic  of  annelid 
muscle  but  disagree  in  the  interpretation.  Straub  claims  that  strips 
of  the  muscles,  both  with  and  without  nerve,  will  give  rhythmic  contrac- 
tions. However,  regions  of  the  worm  from  which  the  nerve  had  been 
removed  must  be  given  several  (eight)  days  for  recuperation  and  then 
they  would  give  contractions  comparable  to  those  of  the  regions  of 
worm  with  nerve  intact.  Budington  found  that  when  care  was  used 
to  remove  all  nervous  tissue  by  using  only  pieces  of  worm  in  which 
the  whole  ventral  muscle  had  been  removed,  that  such  pieces  gave -no 
rhythm ;  while  pieces  containing  even  a  small  amount  of  nerve  gave  a 
regular  rhythmic  curve  (fig.  10). 


1918] 


Bovard:  Nervous  Impulses  in  the  Earthworm 


121 


^-*>-AAM/U^ 


B 


A  =  Short  piece  of  whole  worm  with  nerve  cord. 
B  =  Dorsal  longitudinal  half  without  nerve  cord. 
C  ~  Ventral  longitudinal  half  with  nerve  cord. 

Fig.  10.  Experiment  104.  Curve  A  is  made  by  a  short  piece  of  worm 
attached  to  a  writing  lever.  The  piece  was  normal  in  every  way  and  gave 
rhythmical  contractions.  Curve  B  represents  a  curve  made  by  the  dorsal  half 
of  a  short  piece  of  a  worm  that  had  been  split  in  two  longitudinally.  This 
piece  contained  no  nerve  cord.  Curve  C  was  made  by  the  ventral  half  of  a 
short  piece  of  a  worm  that  had  been  split  in  two  longitudinally.  This  piece 
did  contain  the  ventral  nerve  cord  and  did  give  rhythmic  contractions. 

My  results  agree  entirely  with  those  of  Budington.  It  is  quite 
possible  that  the  findings  of  Straub  may  be  due  to  a  factor  that  he 
overlooked,  the  matter  of  regeneration.  As  I  shall  show  in  a  later 
paper,  regeneration  is  exceedingly  rapid  and  there  is  a  possibility  that 
nerves  have  grown  into  the  operated  portion,  and  the  probability  is 
that  Straub  was  really  dealing  with  pieces  in  which  nerve  fibers  and 
cells  had  regenerated. 

As  further  evidence  of  this  dependence  upon  the  nerve  cord  for 
transmission  it  will  be  noted  that  when  a  worm  is  pinned  in  the  middle 
portion  to  a  cork  plate  and  the  anterior  and  posterior  ends  are  regis- 
tering coordinated  movements  on  a  revolving  drum,  if  the  nerve  be 
cut  in  the  pinned  region  the  rates  of  contraction  of  the  two  parts  will 
be  immediately  changed.  In  this  case,  the  muscle  is  disturbed  as  little 
as  possible  and  only  the  nerve  cord  is  cut  (fig.  11). 


Read  in  this  direction  — > 

Fig.  11.  Shows  how  the  posterior  half  of  the  worm  changed  its  rhythm  after 
the  nerve  cord  had  been  cut.  The  upper  line  represents  the  movements  of  the 
anterior  (-4)  half  and  the  lower  line  the  posterior  (B)  half.  The  nerve  cord 
was  cut  without  cutting  any  but  a  small  portion  of  the  ventral  muscle. 

Conclusion. — From  the  work  just  cited,  it  is  quite  certain  that 
spontaneous  movements  are  dependent  on  the  nervous  tissue  and  that 


122  University  of  California  Publications  in  Zoology      [VOL.  18 

the  muscle  has  no  property  of  rhythmic  contractility.  While  this  does 
not  show  that  transmission  of  impulse  passes  over  many  ganglia  in 
locomotion  it  strengthens  the  work  of  Biedermann  (1904)  and  Bud- 
ington  (1902)  who  hold  the  theory  of  nervous  control. 

RATES  OP  TRANSMISSION  OF  LOCOMOTOB  IMPULSES 

Problem. — The  fact  that  locomotor  impulses  could  be  transmitted 
through  a  portion  of  the  nerve  cord  isolated  from  segmental  muscle 
connections  led  to  the  query,  what  is  the  speed  of  these  impulses  ?  If 
the  speed  were  rapid  it  would  mean  that  there  were  some  fairly  long 
neurones  in  the  cord,  and  if  the  speed  were  slow  it  could  be  interpreted 
on  the  basis  of  short  neurones  and  many  synapses.  This  study  should 
throw  some  light  on  the  structural  basis  of  transmission. 

Discussion. — Jenkins  and  Carlson  (1903)  measured  the  rate  of 
nerve  impulses  in  several  species  of  annelids.  The  rates  were  found 
to  be  exceedingly  variable,  from  89  centimeters  in  Nereis  sp.  to  694 
centimeters  per  second  in  Bispira  polymorpha.  The  question  these 
investigators  raised  was  whether  they  were  dealing  with  simple  con- 
tinuous nerve  fibers  or  with  a  very  complex  nervous  tract.  While  the 
anatomical  connections  of  neurones  in  the  cord  have  been  worked  out 
to  some  fair  degree  of  certainty,  no  long  connections  have  been  estab- 
lished in  the  cord,  except  by  the  giant  fibers.  Jenkins  and  Carlson 
left  the  question  open  as  to  whether  their  measurements  were  those  of 
a  direct  nervous  path  or  an  indirect  one. 

After  observing  a  very  large  number  of  experiments  on  the  trans- 
mission of  the  impulses  as  they  pass  through  the  etherized  section  of  the 
worm,  and  noting  the  slow  progress  of  these  as  compared  to  the  quick 
end  to  end  jerk  of  the  worm  when  stimulated,  there  is  little  doubt 
in  my  own  mind  but  that  the  cord  has  two  kinds  of  transmission  of 
nerve  impulses.  First,  the  very  rapid  impulses  through  giant  fibers, 
which  result  in  vigorous  contractions,  as  in  the  jerking  back  into  their 
burrows  of  the  worms  when  strongly  stimulated ;  and  the  second  type, 
the  impulses  in  the  short  fibers  in  the  middle  of  the  nerve  cord,  which 
offer  a  complex  path  and  so  transmit  impulses  slowly  down  the  cord. 

My  records  for  the  speed  of  impulses  in  the  giant  fibers  agree  quite 
well  with  the  speed  recorded  by  Jenkins  and  Carlson  (1903).  The 
method  which  these  workers  used  was  such  that  only  the  action  of 
quick  contractions  was  recorded  and  no  attempt  was  made  to  separate 
this  phenomenon  from  that  of  the  locomotor  impulses.  As  has  been 
shown,  these  latter  impulses  run  but  short  distances  in  the  cord  unless 


1918] 


Bovard:  Nervous  Impulses  in  the  Earthworm 


123 


reinforced  by  outside  reflexes ;  and  so,  unless  special  methods  are  used, 
the  reactions  of  these  short  fiber  systems  would  not  be  observed. 

A  frequent  observation  on  the  locomotor  habits  of  worms  is  that 
the  wave  of  contraction  runs  for  a  short  distance  and  then  disappears. 
This  was  a  source  of  great  inconvenience  in  determining  the  rate  of 
impulse  down  the  cord.  A  method  was  devised  whereby  electric  con- 
tacts were  successively  made  as  the  wave  of  contraction  passed  along 
the  worm.  These  were  recorded  on  a  drum  from  which  measurements 
were  easily  made  and  speeds  computed  (fig.  12). 


ant 


x.         c.pl 


Fig.  12.  The  apparatus  for  measuring  the  speed  of  nervous  impulses  through 
the  nerve  cord  in  an  anesthetized  region  was  as  follows:  a.l.  and  p.l.  are  levers 
pivoted  at  piv.  The  lower  part  of  the  lever  n  is  a  sharp,  very  fine  needle.  One 
of  these  is  thrust  into  the  muscles  of  the  first  segment  in  front  of  the  anesthet- 
ized part  m.  and  the  other  into  the  muscles  just  behind  this  region  m.  The 
upper  ends  of  these  levers  is  quite  long  so  that  very  slight  movements  of  the 
lower  part  will  produce  considerable  movement  in  the  upper  part.  Platinum 
contacts  were  provided  at  pt.c.  and  each  lever  was  connected  by  battery  to 
signal  magnets,  a.s.  and  p.s.,  which  gave  a  record  on  a  smoked  drum  of  a 
kymograph.  When  the  locomotor  movement  of  the  anterior  part  of  the  worm 
had  reached  the  muscles  at  x.  the  electrical  contact  would  be  made  in  lever  a.l., 
which  registered  on  a  fast  revolving  drum  at  a.s.  Now  when  the  nervous  impulses 
had  passed  through  the  anesthetized  area  m.  and  reached  the  muscle  y.  another 
electrical  contact  was  made  by  lever  p.l.  and  registered  by  signal  magnet  p.s. 
The  speed  of  the  drum  being  measured,  the  speed  of  the  impulse  could  be 
calculated. 


124  University  of  California  Publications  in  Zoology      [VOL.  18 

The  very  noticeable  result  of  this  series  of  experiments  was  the 
great  variability  in  the  speed,  which  seemed  to  depend  on  the  state  of 
irritability  in  the  worm. 

Another  important  fact  seemed  evident  from  these  measurements; 
namely,  the  longer  the  section  of  nerve  measured  the  slower  the  rate 
recorded. 

TIME  TAKEN  TO  TRAVEL  OVER  CERTAIN  LENGTHS  OF  NORMAL  AND 
ANESTHETIZED  WORMS 


EXPERIMENT  180 

EXPERIMENT  162     • 

EXPERIMENT  162 

1 

1  3  live,  20  etherized 
segments 

.26  seconds 

11  live,  20  etherized 
segments 

.90  seconds 

19  live,  20  etherized 
segments 

.68  seconds 

2 

.44 

.50 

.65 

3 

.24 

.64 

.70 

4 

.21 

.60 

.90 

5 

.25 

.34 

.70 

6 

.35 

.34 

.82 

7 

1.02 

.30 

.92 

8 

.72 

.25 

.75 

9 

.13 

.40 

.72 

10 

.08 

.25 

.72 

Average  .370  .452  .760 

1  These  figures  are  calculated  from  experiment   180,   a  series  different  from 
that  in  columns  2  and  3. 

The  method  for  making  these  records  was  not  refined  and  the 
times  recorded  can  only  be  approximations.  The  table  will  show  that 
where  the  length  of  the  portion  of  the  worm  measured  is  increased  the 
time  of  transmission  increases,  but  not  proportionately.  The  full 
significance  of  this  fact  and  its  relation  to  transmission  and  a  new 
theory  of  locomotion  will  be  brought  out  in  a  later  part  of  this  paper. 

In  measuring  the  speed  of  the  impulse  through  the  nerve  cord  in 
a  section  where  the  muscle  had  been  anesthetized,  the  electric  method 
of  measurement  was  quite  effective.  Records  of  slight  movements  of 
the  segments  just  anterior  to  the  inert  section  were  followed  by  the 
registration  of  movements  beginning  in  the  part  immediately  behind 
this  portion.  Here  again  we  meet  great  variability,  depending  on  the 
state  of  excitement  in  the  worm.  If  the  etherized  section  is  greatly 
increased  in  length  the  point  will  eventually  be  reached  when  no 
impulse  comes  through.  Records  through  more  than  twenty  segments 
were  frequent,  but  when  more  than  twenty  segments  were  used,  failure 
resulted  more  often  than  in  fewer  than  twenty.  Measurements  were 
recorded  over  twenty-eight  segments  but  these  seemed  to  be  exceptional 


1918] 


Bovard:  Nervous  Impulses  in  the  Earthworm 


125 


cases.  For  the  most  part,  impulses  passed  along  the  cord  at  the  rate 
of  about  25  millimeters  per  second.  This  represents  the  mode  of  a 
series  of  ninety-one  measurements.  Several  observations  showed  good 
transmission  at  the  rate  of  60  millimeters  per  second,  and  a  few  were 
recorded  in  which  the  rate  was  very  low,  10  millimeters  per  second 
(fig.  13). 


20,. 


3  8 


0  10  ZO  30  40  50  60  70  60  90  100  110 

Fig.  13.  The  frequency  polygon  which  shows  results  of  ninety-one  measure- 
ments of  the  speed  of  locomotor  impulses  through  the  nerve  cord  when  the 
peripheral  nerves  have  been  anesthetized.  The  mode  lies  between  20  and  30 
millimeters  per  second. 

Conclusion. — The  locomotor  impulses  show  no  definite  speed.  The 
most  interesting  feature  is  the  extreme  variability  of  this  movement. 
In  those  cases  where  strength  of  stimulus  is  sufficient  and  other  con- 
ditions are  right  the  speed  may  be  as  fast  as  100  millimeters  per 
second,  and  again  the  speed  may  be  so  slow  that  it  will ., die  out  in  the 
nerve  cord  without  ever  emerging  from  the  anesthetized  region.  I 
have  taken  the  mode  of  the  frequency  polygon  as  against  the  average 
which  shows  that  ordinarily  the  speed  is  about  25  millimeters  per 
second.  The  slowness  and  variableness  are  the  two  main  character- 
istics. 

RATE  OP  IMPULSES  IN  THE  GIANT  FIBERS 

Problem. — How  does  the  rate  of  transmission  of  locomotor  impulses 
compare  with  that  of  the  giant  fiber?  Are  the  rates  such  that  these 
two  phenomena  can  be  ascribed  to  quite  different  systems  of  neurones  ? 
Discussion. — The  method  used  to  measure  the  rate  of  transmission 
of  impulses  in  the  giant  fibers  was  practically  the  same  as  that  used 
in  measuring  locomotor  transmission,  except  that  in  this  case  it  "was 


126 


University  of  California  Publications  in  Zoology      [VOL.  18 


possible  to  use  the  full  length  of  the  worm.  One  characteristic  of  this 
type  of  action  is  that  it  seems  to  be  related  solely  to  the  longitudinal 
muscles  in  contrast  to  that  of  the  locomotor  nerve  fibers  which  set  up 
complex  reactions  in  both  circular  and  longitudinal  muscles. 

Responses  resulting  from  stimulation  of  these  large  fibers  are  always 
exceedingly  rapid  as  compared  with  other  movements  of  the  worms. 
The  reaction  may  be  slight  or  violent,  according  to  the  amount  of 
stimulus  applied,  but  any  response  travels  the  length  of  the  worm  in 
a  very  short  time.  It  is  interesting  to  note  the  antagonistic  relations 
of  the  innervation  of  muscles  when  a  quiescent  worm  is  stimulated 
lightly,  with  a  sharp  needle,  at  the  anterior  end ;  immediately  there  is 
a  response  by  a  relaxation  of  the  circular  muscles  near  the  posterior 
tip  so  that  this  part  is  flattened  and  enlarged.  If  the  stimulus  is  made 
stronger,  this  reaction  will  be  followed  by  a  jerk  of  the  longitudinal 
muscle  and  when  the  stimulus  is  moderately  strong  the  contraction  of 
the  longitudinal  muscle  is  so  quick  and  extensive  that  no  reactions 
of  the  circular  muscle  can  be  detected. 

A  number  of  determinations  for  speed  of  this  rapid  action  are 
recorded  in  the  accompanying  table.  The  range  of  variation  is  large, 
due  in  part  at  least  to  the  methods  of  measurement  and  the  inaccur- 
acies of  the  apparatus  (fig.  14). 


1457 
1404 
1388 

,                    |    4069      | 

420 
365 
342 
ZZO 

990 
77O 
5E4 

1049 
1026 
IO2O 

1870 
1606 
(512 

£915 
2566 

Fig.  14.  Frequency  polygon  which  shows  the  speed  of  impulse  through  giant 
fibers.  The  figures  represent  millimeters  per  second.  The  mode  is  between  1000 
and  1500  millimeters  per  second. 

All  of  these  measurements  were  made  on  the  large  garden  worm, 
Helodrilus  caliginosa,  and  as  nearly  as  possible  under  the  same  con- 
ditions. The  interesting  feature  of  this  array  of  figures  is  that  they 
are  high  compared  to  those  obtained  in  locomotor  transmission.  Ordin- 
arily they  can  be  said  to  be  fifty  times  faster,  and  may  even  be  one 
hundred  times  faster,  than  the  other  type  of  transmission.  The 
mode  for  these  few  measurements  is  around  1500  millimeters  per 
second.  While  this  is  not  so  rapid  as  some  recorded  by  Carlson  and 
Jenkins  (1903)  (table  1),  in  measurements  on  marine  annelids,  it  is 
certain  that  it  belongs  in  the  same  class  of  phenomena  as  they  were 


1918]  Bovard:  Nervous  Impulses  in  the  Earthworm  127 

TABLE  1 

SUMMARY  OF  RATES  IN  WORMS — CARLSON  AND  JENKINS 

Species  Direction  Centimeters  per  sec. 


Cerebratulus   

P 

A 

5.4-  9.0 

Aulastoma  lacustre  

P 

A 

56.0 

Cirratulus  sp  

P 

A 

90.0 

Arenicola   sp  

A 

P 

120.0 

Bispira   polymorpha    

P 

A 

694.0 

Aphrodite  sp  

A 

P 

54.0 

Polynoe  pulchra  

P 

A 

293.0 

Sthenelais  fusca  

P 

A 

205.0 

Eunice  sp  

P 

A 

466.0 

Nereis  sp  

P 

A 

165.0 

Nereis  virens  

P 

A 

89.0 

Nereis  virens  

A 

P 

73.0 

Lumbriconereis  sp.  (a)  

P 

A 

45-241.0 

Lumbriconereis  sp.  (?>)  

P 

A 

49-937.0 

Lumbriconereis  sp.  (c)  

A 

P 

42-160.0 

Glycera  rugosa  

A 

P 

433.0 

Glycera  rugosa  

P 

A 

435.0 

measuring.  None  of  my  measurements  approached  the  highest  speeds 
in  these  marine  forms,  such  as  that  in  Bispira  polymorpha,  viz.,  6940 
millimeters  per  second,  or  even  in  Lumbriconereis  sp.,  viz.,  9370  milli- 
meters per  second,  nor  on  the  other  hand  did  I  find  any  as  slow  as 
that  in  Cerebratulus  at  54  to  90  millimeters.  Several  worms,  Nereis, 
Arenicola,  Sthenelais,  give  averages  about  the  same  as  that  which  I 
found  for  Helodrilus. 

Jenkins  and  Carlson  used  averages  in  obtaining  the  figures  above, 
when  it  would  seem  such  a  variation  in  measurements  occurred  that 
the  mode  is  more  nearly  the  correct  expression.  I  have  used  this  in 
both  series,  that  on  locomotor  transmission  and  on  giant  fiber  action. 

One  feature  of  giant  fiber  action  that  is  easily  noticed  is,  that, 
once  started,  it  always  goes  through  to  the  posterior  end ;  it  never  dies 
out  in  transit  as  the  locomotor  waves  do.  In  cases  where  the  nerve 
cord  has  been  severed,  the  impulse  runs  as  far  as  the  cut,  and  never 
beyond. 

Krawany  (1905)  in  his  discussion  of  the  elements  in  the  central 
nerve  cord  describes  the  relations  of  the  giant  fibers  to  the  association 
cells  in  the  cord.  These  large  fibers  pass  from  end  to  end  of  the  nerve 
cord  and  in  each  ganglion  send  out  branches  which  are  intimately  in 
connection  with  processes  from  association  cells  in  the  middle  group. 
These  cells  which  thus  synapse  with  the  direct  fibers  never  have  cross- 
over connections  but  seem  to  be  entirely  homolateral. 


128  University  of  California  Publications  in  Zoology      [VOL.  18 

The  physiology  of  these  reactions  is  correlated  with  the  anatomy 
of  these  fibers.  The  path  is  a  direct  one  and  the  speed  of  their 
impulses  is  fast,  1500  millimeters  per  second  compared  with  25  milli- 
meters per  second  for  locomotor  reflexes.  The  connections  are  simple 
and  the  reactions  are  concerned  largely  with  the  contractions  of  but 
one  set  of  muscles,  the  longitudinal  muscles.  The  fibers  run  the  full 
length  of  the  cord  and  so  reactions  are  concerned  with  the  whole 
animal.  They  are  single  fibers  and  produce  a  single  action.  There 
is  no  wave  motion  nor  evidences  of  loss  as  the  stimulus  passes  down 
the  cord. 

There  is  no  reason  to  suppose  that  these  fibers  have  anything  to  do 
with  locomotor  reflexes  or  transmission ;  everything  points  to  a  separate 
function  for  these  large  long  fibers. 

Conclusion. — We  have  taken  for  granted  that  Friedlander 's  (1894) 
suggestion  that  the  end  to  end  movements  are  due  to  impulses  carried 
by  the  giant  fibers.  The  results  of  this  work  on  rates  of  transmission 
seem  to  justify  this  supposition.  No  theory  allows  a  nerve  to  have  for 
itself  more  than  one  rate  of  transmission.  The  speed  of  one  type  of 
action  and  the  slowness  of  the  other  would  necessitate  two  kinds  of 
fibers.  The  anatomical  conditions  and  the  physiological  reaction  are 
easily  correlated.  The  large  giant  fibers  are  continuous  structures 
running  the  full  length  of  the  worm  and  capable  of  carrying  the 
impulses  swiftly  from  end  to  end  at  a  normal  rate  of  1500  millimeters 
per  second,  while  in  the  center  of  the  nerve  cord  are  numerous  short 
neurones  running  short  distances  up  and  down  the  cord,  giving  a 
complex  path,  with  slow  speed  of  transmission,  normally  25  milli- 
meters per  second,  such  as  would  be  expected  on  account  of  the 
multiplicity  of  synapses. 


THEORETICAL  CONSIDERATIONS 

The  Nervous  Mechanism. — Some  of  the  most  salient  facts  brought 
out  in  the  study  of  transmission  are:  the  nervous  system  plays  an 
essential  part  in  the  movements  of  locomotion;  the  impulses  respon- 
sible for  the  waves  of  contraction  are  capable  of  running  for  con- 
siderable distances  in  the  cord  and  are  not  confined  to  one  or  two 
segments,  as  indicated  by  Friedlander ;  transmission  may  extend  over 
as  many  as  twenty  segments  without  intervening  muscular  activity, 
the  rate  of  transmission  is  a  variable  one  becoming  slower  as  it  pro- 


1918]  Bovard:  Nervous  Impulses  in  the  Earthworm  129 

ceeds.  The  giant  fibers  have  little  to  do  with  locomotion  and  are 
specialized  for  rapid,  end  to  end  contractions. 

The  excellent  work  of  Krawany  (1905)  on  the  neurones  of  the 
central  system  of  the  worm  and  the  researches  of  Dechant  (1906)  on 
the  peripheral  nervous  system,  together  with  the  great  amount  of 
work  done  by  the  older  writers,  such  as  Bethe  (1903),  Rhode  (1887), 
Apathy  (1897),  Retzius  (1900),  Biedermann  (1904),  Smirnow  (1894), 
and  others,  have  demonstrated  that  the  nervous  system  is  compounded 
of  many  short  neurones.  The  longest  elements  are  some  few  large 
fibers  from  the  anterior  end  of  the  cord  which  arise  in  the  sub- 
esophageal  ganglion  and  run  posteriorly  to  the  terminal  segment,  but 
Krawany  (1905)  shows  that  for  the  most  part  the  other  nerve  fibers 
run  only  from  one  ganglion  to  the  next. 

Sensory  nerve  fibers  originating  in  the  epidermis  pass  down 
through  the  main  nerve  trunks  to  the  ganglion  where  they  branch  as 
T-  or  Y-shaped  bifurcations  immediately  on  entering.  These  run  but 
short  distances  before  ending  in  fine  arborizations.  Krawany  (1905) 
was  unable  to  demonstrate  that  these  passed  into  ganglia  anterior  or 
posterior  to  the  segments  of  entrance,  but  was  inclined  to  think  that 
they  remained  within  the  ganglion  entered.  No  demonstration  of 
neuro-muscular  end  organs  has  ever  been  made  in  the  smooth  muscle 
of  earthworms.  Retzius  (1895)  and  Langdon  (1900)  have  shown,  by 
using  Golgi  methods,  that  nerve  fibers  are  in  among  the  muscle  cells, 
but  Dechant  (1906)  by  using  methylene  blue  was  unable  to  differ- 
entiate any  definite  end  organs.  Many  nerve  fibers  parallel  to  muscle 
can  be  seen,  showing  the  presence  of  abundant  nervous  tissue,  but  all 
fibers  which  looked  like  end  organs  proved  to  run  only  short  distances 
and  could  not  therefore  be  true  nerves.  "While  free  sensory  endings 
in  the  subepithelial  regions  are  not  yet  demonstrated,  Dechant  believes 
they  are  undoubtedly  there. 

After  entering  the  cord  the  sensory  nerves  bifurcate,  one  branch 
passing  up  and  another  down  the  cord  on  the  same  side  as  they  enter. 
They  may  then  form  synapses  with  neurones  of  motor  ganglia  in  the 
anterior,  middle,  or  posterior  groups  of  nerve  cells.  These  large  cells 
send  out  neuraxes  which  may  or  may  not  cross  to  the  opposite  side, 
where  they  leave  by  one  of  the  three  lateral  roots. 

Within  the  cord,  however,  there  are  still  other  paths  open  to 
impulses  entering  by  the  sensory  paths.  The  large  multipolar  cells  are 
the  association  cells  which  show  an  arrangement  into  three  groups,  an 
anterior,  a  middle,  and  a  posterior  group.  Their  function  is  to  connect 


130  University  of  California  Publications  in  Zoology      [VOL.  18 

more  or  less  distant  parts  of  the  ganglion  and  to  interpolate  them- 
selves between  the  sensory  and  motor  elements.  Many  of  these  are 
homolateral  and  some  are  contralateral.  The  greater  number  of  these 
association  cells  are  intraganglionic,  i.e.,  never  leaving  the  segment; 
but  a  few  in  the  anterior  and  posterior  groups  send  processes  into  the 
next  ganglion  and  so  connect  up  the  ganglia  segment  to  segment. 

The  most  interesting  feature  is  that  in  this  nervous  system  there 
are  no  long  nerve  tracts,  the  giant  fibers  excepted.  Impulses  that 
run  the  length  of  the  cord  must  find  their  way  over  a  complex  route 
and  be  necessarily  slow.  We  have  then  a  nervous  system  made  up  of 
many  short  units.  Each  ganglion  is  a  complete  relay  station  capable 
of  receiving  sensory  and  giving  out  the  motor  impulses  necessary  for 
the  functions  of  each  particular  segment.  The  only  connections 
between  the  succeeding  segments  are  association  fibers  in  the  nerve 
cord  and  a  few  motor  fibers  which  Dechant  (1906)  shows.  These 
motor  fibers  take  their  origin  from  a  nerve  arising  from  the  posterior 
root  and  pass  laterally  around  the  muscular  wall  near  the  interseg- 
mental  furrow  and  at  intervals  give  off  five  branches  which  pass  into 
the  segment  behind.  Without  these  two  connections,  one  in  the  cord 
and  one  peripheral,  there  would  be  no  nervous  connection  from  seg- 
ment to  segment  of  the  worm. 

Friedlander  (1894)  laid  particular  emphasis  on  the  "pull"  of  one 
segment  on  the  succeeding  ones  and  that  coordination  was  accom- 
plished even  though  the  nerve  cord  were  cut.  The  experiment  of 
cutting  a  worm  in  two  and  attaching  a  string  to  each  part  resulting 
in  coordinated  movements  indicates  that  pull  certainly  does  play  an 
important  part.  Undoubtedly  the  tension  or  stretching  stimulates 
the  nerve  and  starts  the  reflex  movement.  The  succeeding  movements 
then  are  due  to  both  pull  and  nerve  impulse.  If  part  is  etherized,  it 
ceases  contractions  although  it  responds  to  direct  stimulus.  The  nerve 
reflex  has  been  broken.  Again,  if  tension  be  eliminated  by  pinning 
experiments,  coordinated  movement  proceeds ;  but  if  now  the  nerve  be 
cut,  coordination  ceases.  So  while  tension  is  important  in  supplying 
a  stimulus  to  the  nerve  mechanism,  it  is  not  wholly  sufficient. 

Biedermann  (1904)  showed  that  these  reflexes  can  travel  consider- 
able distances  in  the  cord.  The  interpretation  of  this  might  demand 
that  there  be  present  in  the  nerve  cord  longer  systems  of  neurones 
than  had  been  previously  reported.  However,  it  can  be  shown  that 
no  such  supposition  is  necessary.  The  present  knowledge  of  th^ 
neurones  can  be  used  to  explain  the  facts  at  hand?; 


1918]  Bovard:  Nervous  Impulses  in  the  Earthworm  131 

TRANSMISSION  BY  REINFORCED  STIMULI 

There  is  one  other  point  of  great  importance  in  the  analysis  of 
locomotion  in  the  earthworms  and  one  which  has  not  been  heretofore 
mentioned.  This  is  the  variability  in  the  rate  of  the  impulse  along 
the  cord.  Experiments  have  shown  that  the  transmissions  over  short 
distances  are  much  faster  than  those  over  longer  distances,  and  this 
agrees  with  a  phenomenon  easily  observable  in  the  movements  of 
worms,  i.e.,  the  dying  out  of  waves  of  contraction.  One  can  watch  a 
wave  of  contraction  start  down  the  length  of  the  worm  and  become 
more  and  more  feeble  until  it  is  lost  at  the  middle  region.  The  distance 
the  wave  runs  seems  to  depend  on  the  force  of  the  wave  at  the  start. 
A  strong  wave  runs  further  than  one  with  a  weak  start.  A  glance  back 
at  the  charts  of  the  speeds  of  impulses  passing  through  the  etherized 
portion  of  a  worm  will  show  that  there  is  a  great  variability.  One 
has  but  to  observe  a  single  worm  under  the  experimental  conditions 
to  become  convinced  of  this  without  the  figures. 

Any  theory  that  accounts  for  locomotion  must  take  into  considera- 
tion the  short  unit  system  of  the  nervous  system,  the  transmission  of 
locomotor  impulses  over  long  sections  of  the  cord,  and  the  variability 
in  rate  of  the  speed  of  these  impulses. 

Friendlander  (1894)  likened  the  locomotor  mechanism  to  a  system 
of  telegraphic  relays.  Each  contraction  of  the  circular  muscle  elongated 
the  segment  and  stretched  the  longitudinal  muscle.  This  stretching 
caused  a  stimulus  to  pass  along  the  nerves  to  the  cord,  where  a  reflex 
gave  a  contraction  of  the  longitudinal  muscle.  The  contraction  of  the 
longitudinal  gave  the  pull  which  caused  the  circular  muscle  to  contract 
and  so  on  down  the  length  of  the  worm,  each  segment  with  its  own 
reflex,  but  progression  of  the  wave  of  contraction  due  to  the  pull  of 
contracting  parts  on  succeeding  segments. 

A  short  unit  nervous  system  is  all  that  is  necessary  for  such  an 
explanation.  But  when  transmission  of  locomotor  impulses  can  pass 
along  the  cord  this  relay  system  in  each  segment  is  not  sufficient.  If, 
however,  we  suppose  that  the  association  fibers  transfer  stimuli  from 
one  ganglion  to  the  next,  then  we  have  a  means  for  explaining  Bieder- 
mann's  experiment.  One  of  the  characteristics  of  this  transmission 
was  that  it  varied  considerably  in  rate.  •  When  the  wrorm  was  in  an 
excited  state  or  stimulated,  the  impulses  passed  through  an  etherized 
section  faster  than  otherwise.  If  we  suppose  that  with  each  contrac- 
tion reflexes  are  set  up  in  each  segment  and  that  these  stimuli  entering 
the  cord  reinforce  the  locomotor  stimuli  passing  along  in  the  short 


132  University  of  California  Publications  in  Zoology      [VOL.  18 

association  tracts,  and  that  if  these  stimuli  are  heavy  they  add  to  the 
strength  of  stimulus  passing  along,  or  if  weak  add  little  or  nothing  at 
all,  then  we  have  a  basis  for  explaining  the  variations  in  rate.  In 
each  ganglion  there  will  be  at  least  one  and  maybe  two  synapses  to  be 
passed,  each  with  a  certain  resistance  which  will  tend  to  cu4;  down  the 
force  of  the  stimulus  and  its  power  to  get  through.  Each  synapse  in 
each  segment  resists  the  passage  of  the  locomotor  impulse  but  in 
ordinary  locomotion  each  well  coordinated  contraction  wave  reinforces 
the  loss  and  the  movement  runs  the  full  length  of  the  worm.  The 
uncertain  limit  of  such  transmission  then  can  be  understood  for  many 
factors  may  come  in  to  change  the  force  of  the  stimulus ;  the  stimulus 
may  have  started  in  a  weak  contraction — outside  conditions  may  have 
altered  the  amount  of  reinforcement — internal  conditions  in  the  cord 
itself  may  have  demanded  a  more  complex  path  in  one  case  than  in 
another,  or  even  the  physiological  condition  of  the  worm  may  have  had 
some  effect  on  the  resistance  in  the  synapses. 


SUMMARY 

1.  When  a  worm  is  anesthetized  in  the  middle  area  and  the  peri- 
pheral nerves  are  rendered  useless,  locomotor  impulses  may  be  trans- 
mitted in  both  directions  through  the  nerve  cord  of  this  middle  region 
from  anterior  to  posterior,  and  posterior  to  anterior. 

2.  Tension  or  pull,  while  important  in  normal  creeping  movements, 
may  be  eliminated  and  the  locomotor  stimuli  will  still  pass  up  and 
down  the  cord  for  some  distance. 

3.  Nerve   free   preparations   show   that   locomotor   impulses   may 
travel  considerable  distances  in  the  cord.     Under  such  conditions  the 
anterior  and  posterior  parts  act  in  perfect  coordination.     When  the 
nerve  is  cut  such  coordination  ceases.     Stovaine  when  applied  to  the 
nerve  cord  blocks  the  passage  of  locomotor  impulses  up  and  down  and 
the  coordination  of  anterior  and  posterior  parts  is  lost;  as  soon,  how- 
ever, as  the  effects  of  the  drug  are  removed  impulses  again  pass  freely 
in  the  cord  and  coordination  returns. 

4.  The  results  of  measuring  the  limits  of  transmission  of  the  loco- 
motor  impulses  shows  that  no  absolute  limits  can  be  set.    The  impulses 
travel  short  distances  of  ten  segments  very  readily  but  when  required 
to  traverse  a  longer  section  of  twenty-eight  segments  the  difficulty  is 
great.    No  records  show  impulses  passing  through  as  many  as  thirty 
segments. 


1918]  Bovard:  Nervous  Impulses  in  the  Earthworm  133 

5.  Spontaneous    rhythmical    movements    are    dependent    on    the 
nervous  system  and  the  muscle  tissues  do  not  possess  the  property  of 
rhythmic  contractility.     This  strengthens  the  theory  that  locomotion 
is  under  nervous  control. 

6.  The  speed  of  locomotor  impulses  is  quite  variable.     The  mode 
that  expresses  the  normal  rate  is  about  25  millimeters  per  second.    The 
rate  may  be  increased  or  decreased  in  transit  from  segment  to  segment. 

7.  The  rate  of  the  transmission  of  giant  fiber  action  is  very  rapid 
when  compared  to  that  of  the  locomotor  impulses.     The  mode  for  a 
number  of  measurements  shows  the  speed  to  be  about  the  rate  of  1500 
millimeters  per  second.      The  wide  gap  between  these  two  types  of 
nervous  activity,  the  slow  locomotor  on  the  one  hand  and  the  rapid 
giant   fiber  action   on  the   other,   indicates  that   these   impulses   are 
mediated  by  two  quite  different  kinds  of  nerve  elements. 

8.  The  anatomy  of  the  nerve  cord  as  shown  by  Krawany  and 
Deschant  has  in  it  no  long  neurones.     The  processes  may  join  suc- 
cessive ganglia  but  none  extend  through  the  cord  for  a  great  distance 
except  the  larger  giant  fibers,  which  run  the  full  length  of  the  cord. 

9.  The  peculiarities  of  the  locomotor  impulses  in  transmission,  such 
as  the  variability  in  rate  of  speed,  and  the  slowness  of  it,  can  be 
accounted  for  on  the  basis  of  the  structure.     The  impulse  to  make  its 
way  down  the  cord  must  pass  in  each  ganglion  at  least  one  synapse, 
and  the  possibility  is  that  there  would  be  more  than  this.  Each  synapse 
would  not  only  cut  down  the  strength  of  the  impulse  but  would  also 
slow  down  the  speed  because  of  the  time  consumed  to  cross  the  gap 
between  neurones.      In  normal  creeping  the  impulses  travel   regu- 
larly down  the  cord  because  each  contraction  of  circular  and  longi- 
tudinal muscle  in  each  segment  sends  in  locomotor  impulses  which 
reinforce  the  impulse  passing  down  the  central  nerve  cord,  and  any 
loss  through  the  synapse  is  made  up  in  this  way.     If  for  any  reason 
the  muscular  activity  fail  or  if  the  nervous  connections  to  the  cord  be 
destroyed  the  locomotor  impulse  traveling  down  the  cord  in  this  region 
would  decrease  in  strength  and  decrease  in  rate  because  of  the  lack  of 
reinforcement. 


134  University  of  California  Publications  in  Zoology      [VOL.  18 

LITERATURE  CITED 

APATHY,  S. 

1897.     Das  leitende  Element  des  Nervensystems  und  seine  topographischen 

Beziehungen  zu  den  Zellen.    Mitth.  Zool.  Stat.  Neapel,  12,  495-748, 

pis.  23-32. 
BETHE,  A. 

1903.  Allgemeine   Anatomic   und  Physiologic   des   Nervensystems    (Leipzig, 

Thieme),  vii,  487,  2  pis.,  95  figures  in  text. 

BlEDERMANN,  W. 

1904.  Studien  zur  vergleichenden  Physiologic  der  peristaltischen  Bewegun- 

gen   der  Wiirmer  und   der  Tonus   glatter   Muskeln.     Arch,   gesam. 
Physiol.,  102,  475-542,  1  figure  in  text. 

BUDINGTON,    E.    A. 

1902.  Some  physiological  characteristics  of  annelid  muscles.   Am.  J.  Physiol., 
7,  155-179,  16  figures  in  text. 

DECHANT,  E. 

1906.     Beitrage    zur    Kenntnis    des    peripheren    Nervensystems    des    Begen- 

wurms.     Arb.  Zool.  Inst.  Wien,  16,  361-382,  pis.  1-2,  2  figures  in 

text. 
FRIEDLANDER,  B. 

1894.  Beitrage   zur   Physiologic   des   Centralnervensystems   und   des    Bewe- 

gungsmechanismus   der  Begenwiirmer.     Arch,   gesam.  Physiol.,   58, 

168-206. 
GARREY,  W.  E.  AND  MOORE,  A.  E. 

1915.     Peristalsis  and  coordination  in  the  earthworm.     Am.  J.  Physiol.,  39, 

139-148,  2  figures  in  text. 
JENKINS,  O.  P.  AND  CARLSON,  A.  J. 

1903.  The  rate  of  the  nervous  impulse  in  the  ventral  nerve  cord  of  certain 

worms.     J.  Comp.  Neur.,  13,  259-289,  14  figures  in  text. 
KRAWANY,  J. 

1905.  Untersuchungen  iiber  das  Zentralnervensystem  des  Begenwurms.    Arb. 

Zool.  Inst.  Wien,  15,  281-316,  pis.  1-15,  11  figures  in  text. 
KRUKENBERG,  C.  F.  W. 

1881.     Vergleichend-toxicologische  Untersuchungen  als  experimentelle  Grund- 
lage   fur   eine   Nerven-   und   Muskelphysiologie   der    Evertebraten. 
Vergl.  Physiol.  Studien,  1,  77-155,  1  pi.,  1  figure  in  text. 
LANGDON,  F.  E. 

1900.     The  sense  organs  of  Nereis  virens.    J.  Comp.  Neurol.,  10,  1-77,  3  figures 

in  text. 
BETZIUS,  G. 

1895.  Die  Smirnow'schen  freien  Nervenendigungen  im  Epithel  des  Begen- 

wurms.     Anat.  Anz.,  10,  117-123,  7  figures  in  text. 
1900.     Zur  Kenntnis  des  sensiblen  und  des  sensorischen  Nervensystems  der 

Wiirmer  and  Mollusken.     Biol.  Unters,  9,  83-96,  pis.  16-22. 
EOHDE,  E. 

1887.     Histologische    Untersuchungen    iiber    das    Nervensystem    der    Chaeto- 

poden.     Zool.  Beitrage,  2,  1-81,  pis.  1-7. 
SMIRNOW,  A. 

1894.     Ueber  freie  Nervenendigungen  im  Epithel   des  Begenwurms.      Anat. 

Anz.,  9,  570-578,  3  figures  in  text. 
STRAUB,  W. 

1900.     Zur  Muskelphysiologie  des  Begenwurms.     Arch,  ges  Physiol.,  79,  379- 
399,  15  figures  in  text. 


UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS— (Continued) 

5.  Notes  on  the  Tintinnoina.    1<  On  the  Probable  Origin  of  Diatyocysta  tiara 

Haeckel.     2.  On  Petalotricha  cntsi,  sp.  nov.,  by  Charles  Atwood  Kofoid. 

Pp.  63-69,  8  figures  in  text.    December,  1915 05 

6.  Binary  and  Multiple  Fission  in  Har-amitus,  by  Olive  Swezy.     Pp.  71-88, 

plates  9-11. 

7.  On  a  New  Trichomonad  Flagellate,  Tricliomitus  parvus,  from  the  Intestine 

of  Amphibians,  by  Olive  t  Swezy.    Pp.  89-94,  plate  12. 

Nos.  6  and  7  in  one  cover.    December,  1915 .25 

8.  On  Elcpltarcorys  equi,  sp.  nov.,   a  New  Ciliate  from  the  Caecum  of  the 

Horse,  by  Irwin  C.  Schumacher.    Pp.  95-106,  plate  13.    December,  1915 10 

9.  Three  New  Helices  from  California,  by  S.  Stillmatt  Berry.     Pp.  107-111. 

January,  1916 05 

10.  On'Trypanosoma  triatomae,  a  New  Flagellate  from  a  Hemipteran  Bug  from 

the  Nests  of  the  Wood  Eat  Ncotcma  fuscipcs,  by  Charles  Atwood  Kofoid 

and  Irene  McCulloch.    Pp.  113-126,  plates  14-15.    February,  1916 .15 

11.  The  Genera  Monocercomoiias  and  PolymasUx,  by  Olive  Swezy.    Pp.  127-138, 

plates  18-17.     February,  1916 10 

12.  Notes  on  the  Spiny  Lobster  (Pan-ulirus  intcrrnptus)  of  the  California  Coast, 

by  Bennet  M.  Allen.    Pp.  139-152,  2  figures  in  text.    March,  1916 15 

13.  Notes  on  the  Marine  Fishes  of  California,  by  Carl  L,  Hubbs.    Pp.  153-169, 

platss  18-20.     March,  1916 15 

14.  The  Feeding  Habits  and  Food  of  Pelagic  Copepods  and  the  Question  of 

Nutrition  by  Organic  Substances  in  Solution  in  the  Water,  by  Calvin  O. 
Esterly.    Pp.  171-184,  2  figures  in  text.    March,  1916  .15 

15.  The  Kinetonucletis  of  Flagellates  and  the  Binuclear  Theory  of  Hartmann, 

by  Olive  Swezy.    Pp.  185-240,  58  figures  in  text.    March,  1916  50 

16.  On  the  Life-History  of  a  Soil  Amoeba,  by  Charlie  Woodruff  Wilson,     Pp. 

241-292,  plates  18-23.    July,  1916  ; 60 

17.  Distribution  of  Land  Vertebrates  of  Southeastern  Washington,  by  Lee 

Raymond  Dice.     Pp.  293-348,  plates  24  26.    June,  1916 60 

18.  The  Anatomy  of  Heptanc.lms  maculatus:  the  Endoskeleton,  by  J.  Frank 

Daniel.    Pp.  349-370,  pis.  27-29,  8  text  figures.    December,  1916 25 

19.  Some  Phases  of  Spermatogenesis  in  the  Mouse,  by  Harry  B.  Yocom.    Pp. 

371-380,  plate  30.     January,  1917  10 

20.  Specificity  in  Behavior  and  the  Relation  between  Habits  in  Nature  and 

Reactions  in  the  Laboratory,  by  Calvin  O.  Esterly.    Pp.  381-392.    JMarch, 
1917 , : 10 

21.  The  Occurrence  of  a  Rhythm  in  the  Geotropism  of  Two  Species  of  Plank- 

ton Copepods  when  Certain  Recurring  External  Conditions  are  Absent,  by 
Calvin  O.  Esterly.    Pp.  393-400.    March,  1917 10 

22.  On  Some  New  Species  of  Aphroditidae  from  the  Coast  of  California,  by 

Christine  Essenberg.    Pp.  401-430,  plates  31-37.    March,  1917 35 

23.  Notes  on  the  Natural  History  and  Behavior  of  Emerita  analoga  (Stimpson), 

by  Harold  Tupper  Mead.    Pp.  431-438,  1  text  figure.    April,  1917 .10 

24.  Ascidians  of  the  Littoral  Zone  of  Southern  California,  by  William  E.  Ritter 

and  Ruth  A.  Forsyth.    Pp.  439-512,  plates  38-46.    August,  1917 1.00 

Vol.  17.  1.  Diagnoses  of  Seven  New  Mammals  from  East-Central  California,  by  Joseph 
Grinnell  and  Tracy  I.  Storer.    Pp.  1-8. 

2.  A  New  Bat  of  the  Genus  Myotix  from  the  High  Sierra  Nevada  of  Cali- 

fornia, by  Hilda  Wood  Grinnell.    Pp.  9-10. 

Nos.  1  and  2  in  one  cover.    August,  1916 10 

3.  Spclerpes   platyceplwhtx,   a  New  Alpine   Salamander   from   the   Yosemite 

National  Park,  California,  by  Charles  Lewis  Camp.    Pp.  11-14.    Septem- 
ber, 1916  05 

4.  A  New  Spermophile  from  the  San  Joaquin  Valley,  California,  with  Notes 

on  Ammospermophttus  nelsoni  nelsoni  Merriam,  by  Walter  P.  Taylor.    Pp. 
15-20,  1  figure  in  text.    October,  1916  05 

5.  Habits  and  Food  of  the  Roadrunner  in  California,  by  Harold  0.  Bryant. 

Pp.  21-58,  plates  1-4,  2  figures  in  text.    October,  1916 35 

6.  Description  of  Bufo  canorus,  a  New  Toad  from  the  Yosemite  National  Park, 

by  Charles  Lewis  Camp.    Pp.  59-62,  4  figures  in  text.    November,  1916......      .05 

7.  The  Subspecies  of  Sceloporus  occidentalis,  with  Description  of  a  New  Form 

from   the   Sierra  Nevada   and   Systematic   Notes   on   Other   California 
Lizards,  by  Charles  Lewis  Camp.    Pp.  63-74.    December,  1916 10 

8.  Osteological  Relationships  of  Three   Species  of  Beavers,  by  F.   Harvey 

Holden.    Pp.  75-114,  plates  5-12,  18  text  figures.    March,  1917... .40 

9.  Notes  on  the  Systematic  Status  of  the  Toads  and  Frogs  of  California,  by 

Charles  Lewis  Camp.    Pp.  115-125,  3  text  figures.    February,  1917 10 


UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS— (Continued) 

10.  A  Distributional  List  of  the  Amphibians  and  Reptiles  of  California,  by 

Joseph  Grrinnell  and  Charles  Lewis  Camp.    Pp.  127-208,  14  figures  in  text. 
July,  1917  85 

11.  A  Study  of  the  Races  of  the  White-Fronted  Goose  (Anser  albifrons)  Occur- 

ring in  California,  by  H.  S.  Swarth  and  Harold  C.  Bryant.    Pp.  209-222, 

2  figures  in  text,  plate  13.    October,  1917  .15 

Vol.  18.   1.  Mitosis  in  Giardia  Mieroti,  by  William  C.  Boeck.    Pp.  1-26,  plate  1.    Octo- 
ber, 1917  35 

2.  An  Unusual  Extension  of  the  Distribution  of  the  Shipworm  in  San  Fran- 

cisco Bay,  California,  by  Albert  L.  Barrows.    Pp.  27-43.    December,  1917.      .20 

3.  Description  of  Some  New  Species  of  Polynoldae  from  the  Coast  of  Cali- 

fornia, by  Christine  Essenberg.    Pp.  45-60,  plates  2-3.    October,  1917 .20 

4.  New  Species  of  Amphinomida,c  from  the  Pacific  Coast,  by  Christine  Essen- 

berg.    Pp.  61-74,  plates  4-5.    October,  1917  .15 

5.  CritMdia  fhiryophthalmi,  sp.  nov.,  from  the  Hemipteran  Bug,  EuryopMhalmus 

Convivus  Stal,  by  Irene  McCulloch.  •  Pp.  75-88,  35  text  figures.     Decem- 
ber,  1917   , 15 

6.  On  the  Orientation  of  Erythropsis,  by  Charles  Atwood  Kofoid  and  Olive 

Swezy.  Pp.  89-102,  12  figures  in  text.    December,  1917 15 

7.  The  Transmission  of  Nervous  Impulses  in  Relation  to  Locomotion  in  the 

Earthworm,  by  John  F.  Bovard.    Pp.  103-134,  14  figures  in  text.    January, 
1918 - 35 

8.  The  Function  of  the  Giant  Fibers  in  Earthworms,  by  John  F.  Bovard.    Pp. 

135-144,  1  figure  in  text.    January,  1918  (In  press) 

9.  A  Rapid  Method  for  the  Detection  of  Protozoan  Cysts  in  Mammalian 

Faeces,  by  William  C.  Boeck.    Pp.  145-149.    December,  1917 05 


UNIVERSITY    OF   CALIFORNIA    PUBLICATIONS 

IN  , 

ZOOLOGY 

Vol.  18,  No.  8,  pp.  135-144,  1  figure  in  text  January  10,  1918 


THE  FUNCTION  OF  THE  GIANT  FIBERS 
IN  EARTHWORMS 


BY 
JOHN   F.  BOVARD 


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VoL  14.  1.  A  Report  upon  the  Physical  Conditions  in  San  Francisco  Bay,  Based  upon 
the  Operations  of  the  United  States  Fisheries  Steamer  "Albatross"  dur- 
ing the  Years  1912  and  1913,  by  F.  B.  Sumner,  G.  D.  Louderback,  W.  L. 
Schmitt,  E.  C.  Johnston.  Pp.  1-198,  plates  1-13,  20  text  figures.  July, 
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1.  Hydrographic,  Plankton,  and  Dredging  Records  of  the  Scripps  Institution 

for  Biological  Research  of  the  University  of  California,  1901  to  1912, 
compiled  and  arranged  under  the  supervision  of  W.  E.  Ritter  by  Ellis 
L.  Michael  and  George  F.  McEwen.  Pp.  1-206,  4  text  figures  and  map. 
July,  1915  2.25 

2.  Continuation  of  Hydrographic,  Plankton,   and  Dredging  Records  of  the 

Scripps  Institution  for  Biological  Research  of  the  University  of  Cali- 
fornia (1913-1915),  compiled  and  arranged  under  the  supervision  of  W. 
E.  Ritter,  by  Ellis  L.  Michael,  Zoologist  and  Administrative  Assistant, 
George  T.  McEwen,  Hydrographer.  Pp.  207-254,  7  figures  in  text.  Novem- 
ber, 1916 : 50 

3.  Summary  and  Interpretation  of  the  Hydrographic  Observations  made  by 

the  Scripps  Institution  for  Biological  Research  of  the  University  of  Cali- 
fornia, 1908  to  1915,  by  George  F.  McEwen,  Hydrographer.  Pp.  255-356, 

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Vol.  16.  1.  An  Outline  of  the  Morphology  and  Life  History  of  Crithidia  leptocoridis, 
sp.  nov.,  by  Irene  McCulloch.  Pp.  1-22,  plates  1-4,  1  text  figure.  Sep- 
tember, 1915  25 

2.  On  Giardla  microti,  sp.  nov.,  from  the  Meadow  Mouse,  by  Charles  Atwood 

Kofoid  and  Elizabeth  Bohn  Christiansen.    Pp.  23-29,  1  figure  in  text. 

3.  On  Binary  and  Multiple  Fission  in   Giardia  muris   (Grassi),   by  Charles 

Atwood  Kofoid  and  Elizabeth  Bohn  Christiansen.  Pp.  30-54,  plates,  5-8, 
1  figure  in  text. 

Nos.  2  and  3  in  one  cover.    November,  1915  30 

4.  The  Cultivation  of  Tissues  from  Amphibians,  by  John  C.  Johnson.    Pp.  55- 

62,  2  figures  in  text.    November,  1915  10 


UNIVERSITY  OF  CALIFORNIA   PUBLICATIONS 

IN 

ZOOLOGY 

Vol.  18,  No.  8,  pp.  135-144,  1  figure  in  text  January  10,  1918 


THE  FUNCTION  OF  THE  GIANT  FIBERS 
IN  EARTHWORMS 


BY 

JOHN  F.  BOVAED 


CONTENTS 

PAGE 

Introduction : 136 

I.  General  functions  of  the  nerve  cord  136 

1.  Biedermann's  theory  136 

2.  Muscle  not  responsible  for  rhythmic  movements  136 

3.  Friedlander 's  theory  of  giant  fiber  action  136 

Materials  and  methods  137 

I.  Material  used 137 

II.  Methods  used  137 

1.  Simple  transection  137 

2.  Eemoval  of  short  sections  of  the  cord  137 

.3.  Effects  of  the  operation  and  recovery  138 

Eegeneration  experiments  138 

I.  Effects  of  simple  transverse  section  138 

1.  Eecovery  of  activity  of  locomotor  fibers  139 

2.  Eecovery  of  activity  of  giant  fibers  139 

II.  Eemoval  of  short  pieces  of  the  cord  140 

1.  Eecovery  of  locomotor  fiber  activity  141 

2.  Eecovery  of  giant  fiber  activity 142 

III.  Comparison  of  results  with  those  of  Straub  and  Friedlander 142 

Experiments  with  stovaine  143 

I.  Methods  143 

II.  Eecovery  from  effects  of  drugs  143 

1.  Behavior  of  the  locomotor  fibers  143 

2.  Behavior  of  the  giant  fibers 143 

Summary    144 

Literature  Cited  ..                                                                                  144 


136  University  of  California  Publications  in  Zoology      [VOL-  18 


INTRODUCTION 

In  the  analysis  of  the  locomotion  of  the  earthworm  Friedlander 
(1894)  showed  that  worms  made  well  co-ordinated  movements  even 
after  considerable  portions  of  their  nerve  cords  had  been  removed. 
He  concluded  that  the  nervous  system  served  simply  as  a  medium  for 
very  short  relayed  reflexes  and  played  a  secondary  part  in  locomotion. 
Biedermann  (1904)  extended  this  idea  by  showing  that  stimuli  could 
run  long  distances  in  the  cord,  and  in  my  recent  paper  (1918)  I  was 
able  to  show  something  concerning  the  limits  of  this  transmission  and 
also  the  rate  at  which  such  impulses  travel  in  the  cord  when  not 
reinforced  from  without. 

Straub  (1900)  claimed  that  the  spontaneous  contractions  of  short 
sections  of  earthworm  were  due  to  inherent  qualities  of  the  muscle ; 
at  least  they  were  not  due  to  the  nervous  system  present.  My  own 
experiments  seemed  to  show  a  contrary  result,  and  in  all  cases  rhythmic 
movements  were  only  in  pieces  containing  nerve  cord. 

The  results  of  these  experiments  just  cited  were  obtained  on  worms 
from  which  the  nerve  cord  had  been  entirely  taken  away.  It  occurred 
to  me,  therefore,  to  study  the  effects  of  regenerating  nerve  cord  on 
locomotor  movements.  It  is  well  known  that  the  nerves  do  not  all 
regenerate  in  the  same  time,  and  this,  then,  would  give  me  some  clue 
as  to  which  fibers  carried  locomotor  responses  and  which  the  end  to 
end  collapsing  movements.  Friedlander  (1894)  suggested  that  the 
quick  jerks  which  take  the  animal  back  into  its  burrow  were  due  to 
impulses  carried  by  the  giant  fibers.  This  has  been  accepted  as  most 
probable,  but  has  not  been  demonstrated.  If,  then,  a  regeneration  of 
the  nerve  cord  would  give  a  differential  healing,  it  would  be  probable 
that  the  giant  fibers  would  unite  sooner  or  later  than  the  transmission 
nerves,  and  we  would  have  some  definite  proof  for  Friedlander 's 
contention. 

The  effects  of  simple  transverse  sections  of  the  ventral  cord  were 
studied  and  later  short  portions  of  the  cord  were  removed.  Drugs, 
such  as  stovaine,  were  also  tested,  because  they  have  the  effect  of 
"blocking"  the  nerve  cord,  which  is  practically  the  same  as  removal 
of  ganglia  for  a  brief  time.  Drugs  have  the  added  advantage  of  losing 
their  effect  quickly,  and  so  the  changes  in  nerve  reactions  during 
development  and  recovery  from  the  anesthesia  could  be  watched. 


19183  Bovard:  Giant  Fibers  in  Earthworms  137 


MATERIALS  AND  METHODS 

Material. — Both  the  common  Allolobophora  foetida  and  Helodrilus 
caliginosa  were  used  in  these  experiments.  Similar  results  were  ob- 
tained with  each,  but  in  general  the  larger  worm  was  the  easier  to 
work  with,  especially  when  operations  were  made  for  the  removal  of 
sections  of  cord. 

Methods. — In  all  cases  where  operations  were  to  be  performed  the 
worms  were  kept  for  at  least  twenty-four  hours  in  clean  moist  cloths, 
so  they  would  clear  themselves  of  dirt  and  grit.  Worms  that  were 
kept  in  moist  filter  paper  usually  ate  large  quantities  of  this,  which 
made  the  cutting  of  sections  quite  difficult. 

The  transecting  of  the  nerve  cord  was  a  simple  operation.  The 
worm  was  held  tightly  on  a  moist  surface  and  a  transverse  cut  made 
with  a  safety  razor  blade.  A  single  stroke  was  usually  sufficient  to 
cut  both  ventral  muscle  and  the  nerve,  and  if  care  were  exercised 
there  was  little  danger  of  cutting  too  deep.  The  cut  was  examined 
with  a  hand-lens  to  make  certain  that  the  cord  had  been  cut. 

A  simple  physiological  method  of  determining  whether  the  cord 
had  been  sectioned,  and  a  method  that  proved  a  check  on  all  experi- 
ments, was  as  follows :  Examination  of  the  worm  immediately  after 
the  operation  showed  that  the  muscles  posterior  to  the  cut  had  lost 
their  tone,  giving  an  increase  in  the  diameter  of  the  part.  This  con- 
dition did  not  extend  for  any  great  distance,  but  was  usually  confined 
to  from  three  to  five  segments.  If  the  nerve  had  not  been  severed, 
this  effect  wore  off  after  the  first  day  of  regeneration;  otherwise  it 
remained  enlarged  until  physiological  continuity  was  re-established. 

In  operating  on  Helodrilus,  a  simple  transverse  cut  with  a  razor 
blade  usually  only  severed  the  musculature.  The  cord  adheres  very 
closely  to  the  intestine  and  comes  away  from  its  ventral  muscles  very 
readily.  In  these  cases  it  was  necessary  to  cut  the  cord  with  a  pair 
of  fine  scissors,  making  a  simple  snip.  Where  care  was  not  used  and 
the  ventral  blood  vessels  were  cut  also,  the  animal  bled  profusely,  and 
in  many  cases  died  or  autotomized  the  posterior  piece. 

When  necessary  to  remove  two  ganglia,  the  worms  were  anesthet- 
ized in  a  5  per  cent  alcohol  solution  for  fifteen  minutes  to  one-half 
hour,  in  all  cases  until  they  were  motionless.  Under  a  dissecting 
microscope,  a  transverse  cut  was  made  in  the  ventral  muscles.  The 
opening  was  stretched  and  pinned  back  with  clean,  fine  needles.  The 
nerve  cord  and  bloodvessels  then  could  be  easily  seen.  Great  care 


138  University  of  California  Publications  in  Zoology      [VOL.  18 

had  to  be  exercised  to  prevent  cutting  any  blood  vessels.  The  cord 
was  lifted  up  with  fine  forceps,  and  a  cut  made  anteriorly.  The  cord 
could  then  be  pulled  forwards  and  a  cut  made  posteriorly.  The  seg- 
ment, which  was  removed,  was  then  put  into  95  per  cent  alcohol  and 
examined  later  to  ascertain  the  exact  amount  of  nerve  substance  re- 
moved. 

After  the  operation  the  worms  were  placed  in  small  8-ounce  jars 
with  some  moist  cloths  over  them  and  put  away  in  a  dark  cabinet. 
It  was  not  found  necessary  to  keep  the  worms  in  a  particularly  cool 
place  as  long  as  the  jars  and  cloths  were  kept  scrupulously  clean.  The 
temperature  was  the  ordinary  room  temperature  during  April  and 
May  in  the  Harvard  laboratories.  The  only  cases  where  worms  died 
during  these  experiments  were  those  which  bled  profusely  after  the 
operation  due  to  rupture  of  the  large  ventral  blood  vessel.  The  loss 
was  surprisingly  small. 

By  the  following  day  the  worms  appeared  normal,  the  wound  had 
healed  over  and  they  could  be  seen  creeping  about  in  the  jars.  Usually, 
however,  they  were  not  very  active  in  the  cramped  quarters  of  their 
jars. 

EFFECT  OF  TRANSVERSE  SECTIONS  OF  THE  CORD 
The  result  of  simply  transecting  the  cord  was  the  loss  of  trans- 
mission and  of  the  animal's  power  to  reverse  its  direction  of  creeping 
on  stimulation.  Stimuli  applied  at  either  end  ran  as  far  as  the  cut, 
but  failed  to  pass  across  the  break  in  the  cord.  Earthworms  often 
respond  to  strong  stimuli  given  to  the  anterior  end  by  certain  lashing 
movements  and  side  to  side  jerks.  When  the  cord  was  severed  these 
lashing  movements  could  be  induced  in  the  anterior  portion  of  the 
worm  without  producing  any  effect  on  the  posterior  part  behind  the 
cut,  which  might  lie  quiet  during  this  movement.  Giant  fiber  action 
induced  either  from  the  anterior  or  the  posterior  direction  was  effective 
as  far  as  the  cut  only.  The  quick,  end  to  end  action  never  succeeded 
in  starting  the  same  kind  of  a  movement  in  the  portion  of  the  worm 
on  the  other  side  of  the  break  opposite  to  the  point  stimulated. 

The  effects  on  the  musculature  were  particularly  noticeable.  Im- 
mediately behind  the  cut  region  the  worm  showed  an  enlargement  of 
the  segments.  Here  the  circular  muscles  seemed  to  have  lost  then 
tone  As  the  worm  crept  along  the  posterior  part  acted  in  co-ordi- 
nation with  the  anterior,  but  these  few  segments  behind  the  cut  took 
no  part  The  length  of  this  inactive  part  varies  from  three  to  five 


1918]  Bovard:  Giant  Fibers  in  Earthworms  139 

segments.  Behind  this,  normal  creeping  movements  were  seen  as  the 
nerve  regenerated  and  the  lost  function  was  restored.  This  appear- 
ance of  the  cut  region  disappeared  as  the  normal  reactions  returned. 


REGENERATION 

The  regeneration  of  the  nerve  was  remarkably  rapid.  Sections 
of  a  worm  (Allolobophora  foetida)  prepared  after  two  days  of  regener- 
ation showed  that  the  nerve  fibers  had  penetrated  into  the  regenerating 
tissue  and  had  formed  across  the  gap.  And  on  the  third  day  the 
physiological  reactions  were  being  transmitted  up  and  down  the  cord. 
The  reversal  of  the  direction  of  creeping  was  easily  possible  on  stim- 
ulation. The  giant  fiber  reactions,  however,  were  not  yet  possible. 
Any  stimuli  which  called  out  such  reactions  in  the  anterior  part  of 
the  worm  ran  only  as  far  as  the  cut,  and  the  same  is  true  of  reactions 
started  in  the  posterior  part.  However,  on  the  fourth  day  and  fifth 
day  the  giant  fiber  action  was  restored  for  the  entire  worm,  which  in 
all  respects  gave  normal  reactions. 

In  the  large  Helodrilus,  the  same  relations  were  found,  except  that 
the  period  of  regeneration  was  a  little  longer.  The  return  of  the 
locomotor  transmission  occurred  usually  from  the  fourth  to  sixth  day 
after  the  operation  and  the  giant  fiber  action  on  the  following  day. 
The  regeneration  of  nerve  cord  in  this  large  worm  shows  a  very  inter- 
esting thing  in  this  return  of  the  activity  of  the  giant  fibers.  Twenty- 
four  hours  after  the  return  of  locomotor  transmission,  one  can  look 
for  giant  fiber  action.  This  makes  its  first  appearance  as  an  impulse 
traveling  from  anterior  to  posterior,  and  it  is  not  until  some  hours 
later,  usually  the  following  day,  that  this  action  is  transmitted  in  the 
opposite  or  postero-anterior  direction. 

In  testing  worms  for  the  return  of  locomotor  transmission  through 
the  cut  area  it  will  be  noticed  that  in  the  early  stages  posterior  creep- 
ing may  not  be  the  response  on  stimulating  the  anterior  part.  How- 
ever, if  several  stimuli  are  given,  summation  takes  place  and  a  pos- 
terior movement  takes  place.  At  other  times  the  result  of  a  stimu- 
lation may  be  shown  in  the  contraction  of  the  circular  muscles  and 
elongation  of  the  posterior  tip,  a  movement  preparatory  to  creeping, 
without  the  movement  being  completed  by  a  well  organized  reaction. 

The  first  indication  of  the  return  of  giant  fiber  transmission  is  a 
condition  that  shows  the  antagonistic  innervation  of  muscles  that  has 
been  shown  for  vertebrates. 


140  University  of  California  Publications  in  Zoology      [VOL.  18 

The  following  table,  no.  182,  shows  a  series  of  worms  and  regen- 
eration of  nerve  cord  as  expressed  by  the  return  of  physiological 
activity. 


EXPERIMENT  182 — EEGENERATION  OF  NERVE  CORD  AFTER  A  SIMPLE  TRANSVESE 

SECTION 

Time  in  days  when  impulses  are  again  possible  in  Transmission  Fibers  and  Giant  Fibers 

Worm 
A 
B 
C 
D 
E 
F 
G 
H 
I 
J 
K 
L 
M 
N 

A     P  —  transmission  from  anterior  end  to  posterior  end. 
P     A  —  transmission  from  posterior  end  to  anterior  end. 


Stimulation  of  the  anterior  end  causes  the  end  to  end  jerk  of 
muscles  as  far  as  the  cut,  but  behind  this  no  such  movement  arises. 
With  each  stimulus  there  will  be  seen,  in  the  posterior  tip,  a  relaxation 
of  the  circular  muscles  and  a  dorso-ventral  flattening.  The  chaetae 
will  be  projected  and  directed  forwards,  but  there  is  no  movement  of 
the  longitudinal  muscles.  A  few  hours  later  the  same  movement  will 
be  accompanied  by  a  distinct  jerk  of  the  longitudinal  muscle,  and  the 
next  day  a  well  co-ordinated,  end  to  end  contraction  will  be  added  to 
the  reaction. 

REMOVAL  OF  SECTIONS  OF  THE  CORD 

When  small  sections  of  the  cord  were  removed,  as  shown  in  the 
following  table,  the  return  of  physiological  activity  was  in  the  same 
order  as  when  simple  transverse  sections  were  made.  The  time  for 
regeneration  and  complete  recovery  was  lengthened,  but  was  still  sur- 
prisingly short. 


Locomotor 
trans. 
A     P 

Locomotor 
trans. 
P     A 

Giant 
fiber 
A     P 

Giant 
fiber 
P     A 

3 

3 

3 



3 

3 





3 

3 

4 

5 

3 

3 

5 

6 

3 

3 

4 

5 

4 

4 

5 

6 

4 

4 

5 

7 

4 

4 

5 

6 

4 

4 

5 

5 

4 

5 

"s 

10 

4 

4 

5 

5 

5 

5 

6 

6 

5 

7 

10 



5 

5 

6 

8 

1918] 


Bovard:  Giant  Fibers  in  Earthworms 


141 


EXPERIMENT  191 — REGENERATION  OF  NERVE  CORD  AFTER  REMOVAL  OF  SHORT 

SECTIONS  OF  CORD 

Giant 
fiber 
P  A 

9 
11 


6(1)9 
9 

13 
6 


11 

6(?)9 


Worm 

No.  of               Trans, 
ganglia           locomotor 
removed              A     P 

Locomotor 
trans. 
P     A 

Giant 
fiber 
A      P 

A 

2                     6 

6 

9 

B 

11                   4 

4 

10 

C 

2 

Dead 

.... 

D 

21 

Dead 

.... 

E 

H                   4 

4 

5 

F 

2                     4 

4 

9 

G 

11 

Dead 

H 

1                      9 

9 

12 

I 

H                   4 

4 

5 

J 

1 

Dead 

K 

1 

Dead 

.... 

L 

2                      9 

9 

10 

N 

2                     4 

4 

5 

A     P  refers 
P     A  refers 

to  loeomotor  impulses  passing 
to  locomotor  impulses  passing 

from  anterior  to 
from  posterior  to 

posterior, 
anterior. 

•  j       • .-, 
-  -  int.  epith. 


n.  sh. 

g-.f. 


-*-•  —  n.  c. 


ctx. 


I.  m. 
cr.  m. 
ch.  sh. 


—  spi. 


Fig-  1 — A  camera  lucida  drawing  showing  the  union  of  the  cut  ends  of  the 
ventral  nerve  cord.  X  42.  Experiment  191,  line  1.  In  this  worm  two  ganglia 
had  been  removed  and  nine  days  given  for  regeneration.  Normal  locomotor 
transmission  and  giant  fiber  action  had  returned,  ch.  sh.,  chaeta  sheath;  dr.  m., 
circular  muscle;  ctx.,  cicatrix  tissue;  epi.,  epidermis;  g.  f .,  giant- fiber;  int.  epith., 
intestinal  epithelium;  I.  m.,  longitudinal  muscle;  n.  c.,  nerve  cord;  n.  sh.,  nerve 
sheath. 


142  University  of  California  Publications  in  Zoology      [VOL.  18 

Figure  1  shows  a  longitudinal  section  of  a  worm  that  showed 
normal  locomotor  transmission  and  giant  fiber  action  after  nine  days 
of  regeneration.  Two  ganglia  had  been  removed.  In  some  cases  the 
regeneration  was  more  rapid  and  in  some  slower,  so  this  figure  repre- 
sents a  typical  case. 

It  was  expected  that  the  removal  of  short  sections  of  the  cord 
would  lengthen  the  time  between  recovery  for  locomotor  transmission 
and  giant  fiber  action.  But  this  was  found  not  to  be  the  case,  for,  in 
general,  the  responses  of  end  to  end  contractions  recur  about  twenty- 
four  hours  after  the  locomotor  transmission  reappears.  Here,  as  in 
the  regeneration  from  simple  transection,  the  giant  fibers  gave  impulses 
in  the  antero-posterior  direction  in  advance  of  those  in  the  opposite 
direction.  While  removal  of  short  pieces  of  cord  lengthens  that  period 
of  regeneration  in  which  no  transmission  of  impulses  is  possible,  it 
changes  very  little  the  order  and  time  of  events  after  the  union  of  the 
cord  is  established. 

The  remarkable  facility  with  which  these  worms  regenerate  lost 
sections  of  nerve  cord  has  an  interesting  bearing  in  the  experiments 
of  Friedlander  (1894)  and  Straub  (1900). 

After  the  removal  of  ten  to  twelve  ganglia  from  the  nerve  cord, 
Friedlander  (1894)  allowed  the  worm  two  to  four  weeks  before  he 
discarded  them  for  use  in  his  experiments.  My  results  would  indicate 
that  he  was  not  dealing  with  segments  entirely  free  from  nervous 
transmission,  for,  while  the  nerve  cord  may  not  have  entirely  regen- 
erated, it  is  certain  that  it  could  have  grown  considerable  distances 
into  the  region,  even  if  it  had  not  grown  across  the  gap.  This  would 
make  a  marked  difference  in  interpreting  experiments  of  co-ordination 
of  anterior  and  posterior  pieces,  especially  if  nearly  four  weeks  had 
been  given  for  regeneration. 

Straub  (1900)  claimed  that  annelid  muscle  would  give  rhythmic 
contraction  if  the  nerve  cord  were  dissected  out.  In  this  case,  sections 
of  twenty  to  thirty  ganglia  were  removed  and  the  worms  given  eight 
days  to  recuperate.  In  this  short  time  the  nerve  probably  could  not 
grow  the  length  of  such  a  gap,  but  could  grow  into  the  area  for  a 
considerable  distance  from  the  end  of  the  nerve  stump.  When  he  cut 
out  the  operated  part  and  used  this  to  show  rhythmic  contractions, 
it  is  just  possible  these  segments  may  have  contained  some  regenerated 
nerve  elements.  Budington  (1902)  has  shown  that  segments  of  worms 
containing  even  small  fragments  of  nerve  will  give  these  rhythmic 
contractions,  but  when  the  ventral  wall  is  removed  no  such  contrac- 
tions can  be  induced. 


1918 J  Bovard:  Giant  Fibers  in  Earthworms  143 


EFFECT  OF  DRUGS 

If  small  quantities  of  cocaine  or  stovaine  are  injected  into  the 
body  cavity  of  the  worm  the  drugs  act  as  a  block  on  the  nerve  and 
affect  the  transmission  through  the  nerve  cord.  Cocaine  has  a  more 
general  effect  on  the  worm  and  produces  in  many  cases  very  irregular 
behavior,  but  stovaine  gives  very  consistent  results.  The  first  effect 
was  the  loss  of  giant  fiber  action  through  the  region.  Transmission 
was  perfect  above  and  below  the  point  of  injection.  As  the  effect  of 
the  drug  worked  deeper  into  the  cord  the  transmission  of  locomotor 
impulses  became  more  irregular  and  in  some  cases  was  lost  altogether. 
As  recovery  took  place  the  return  of  activity  was  just  the  reverse. 
The  locomotor  impulses  became  more  and  more  regular  until  perfect 
co-ordination  was  set  up.  Then  the  giant  fiber  action  began  to  show 
transmissions.  Here,  too,  the  same  phenomena  were  seen  as  in  the 
case  of  regeneration.  Just  before  giant  fiber  impulses  showed  normal, 
end  to  end  responses,  the  stimulation  of  the  anterior  end  showed  the 
characteristic  relaxation  of  the  circular  muscles  in  the  posterior  tip. 
Very  soon  after  this  the  end  to  end  movements  occur  in  response  to 
stimuli. 

A  record  is  given  below  of  an  experiment  with  stovaine,  which 
shows  the  course  of  events  and  the  relation  between  giant  fiber  and 
locomotor  fibers. 


EXPERIMENT  188 — EFFECT  OF  STOVAINE  ON  TRANSMISSION 

May  18,  1915,  4:45  p.m. — The  worm  (Helodrilus  caliginosa},  doubly  pinned  to  a 
cork  plate  on  a  glass,  was  injected  with  a  small  quantity  of  stovaine  in 
the  body  cavity  of  the  middle  region. 

Almost   immediately  giant   fiber   action   is  lost   and   locomotor   trans- 
mission not  normal. 

5:00  p.m. — Locomotor  impulses  pass  through  block,  but  do  not  run  full  length 
of  posterior  part. 

Locomotor  co-ordination  between  anterior  and  posterior  parts. 
As  time  goes  on  locomotor  movements  run  further  down  the  posterior 
part. 

5:10  p.m. — Any  stimulus  to  the  anterior  end  results  in  locomotor  movements 
in  posterior  end.  Wave  contractions  run  to  posterior  tip  more  frequently. 
No  giant  fiber  action. 

5:35  p.m. — Stimulation  of  anterior  end  gives  increased  activity  of  posterior 
end.    No  giant  fiber  action.    Animal  apparently  normal  except  no  end  to 
end  contractions. 
5:48  p.m. — Giant  fiber  action  returned.     Animal  fully  recovered. 


144  University  of  California  Publications  in  Zoology      [V<>L- 18 


SUMMARY 

1.  After  transverse  section  of  nerve  cord,  locomotor  transmission 
fibers  regenerate  before  giant  fibers. 

2.  The  period  of  regeneration  after  a  simple  transection  is  very 
short,  from  three  to  four  days. 

3.  Removal  of  short  pieces  of  the  cord  gives  the  same  results  as 
simple  transverse  section,  except  that  the  period  of  regeneration  is 
prolonged. 

4.  The  effect  of  drugs,  such  as  stovaine,  on  the  cord  shows  that 
the  transmission  fibers  may  be  active,  while  the  giant  fibers  are  still 
under  the  anesthetic.     Recovery  is  in  the  same  order  as  is  shown  in 
regeneration. 

5.  The  general  result  of  this  study  shows  that  the  giant  fibers  are 
concerned  with  other  functions  than  locomotion,  and  that  locomotor 
transmission  fibers  lie  deep  in  the  cord. 


LITERATURE  CITED 

BlEDERMANN,  W. 

1904.     Studien  zur  vergleichenden  Physiologie  der  peristaltischen  Bewegun- 
gen.    I.  Die  peristaltischen  Bewegungen  der  Wiirmer  und  der  Tonus 
glatter  Muskeln.  Arch.  ges.  Physiol.,  102,  475-542,  1  figure  in  text. 
BOVAED,  J.  F. 

1918.     The  transmission  of  nervous  impulses  in  relation  to  locomotion  in  the 

earthworm.     Univ.  Calif.  Publ.  Zool.,  18,  103-134,  14. 
BUDINGTON,  B.  A. 

1902.     Some  physiological  characteristics  of  annelid  muscle.    Am.  J.  Physiol., 
7,  155-179,  16  figures  in  text. 

FRIEDLANDER,  B. 

1894.     Beitrage  zur  Physiologie  des  Centralnerven  systems  und  des  Bewe- 
gungsmechanismus    der    Eegenwiirmer.      Arch.    ges.    Physiol.,    58, 
168-206. 
STRAUS,  W. 

1900.     Zur    Muskelphysiologie    des    Eegenwurms.      Arch.    ges.    Physiol.,    79, 
379-399,  15  figures  in  text. 


UNIVEESITY  OF  CALIFORNIA  PUBLICATIONS— (Continued) 

5.  Notes  on  the  Tintinnoina.    1.  On  the  Probable  Origin  of  Dictyocysta  tiara 

Haeckel.     2.  On  Petalotricha  entzi,  sp.  nov.,  by  Charles  Atwood  Kofoid. 

Pp.  63-69,  8  figures  in  text.    December,  1915  05 

6.  Binary  and  Multiple  Fission  in  Hexamitus,  by  Olive  Swezy.     Pp.  71-88, 

plates  9-11. 

7.  On  a  New  Trichomonad  Flagellate,  Trichomitns  parvus,  from  the  Intestine 

of  Amphibians,  by  Olive  Swezy.    Pp.  89-94,  plate  12. 

Nos.  6  and  7  in  one  cover.    December,  1915  25 

8.  On  Blepharcorys  equi,  sp.  nov.,   a  New  Ciliate  from  the  Caecum  of  the 

Horse,  by  Irwin  C.  Schumacher.    Pp.  95-106,  plate  13.    December,  1915 10 

9.  Three  New  Helices  from  California,  by  S.  Stillman  Berry.     Pp.  107-111. 

January,  1916  , 05 

10.  On  Trypanosoma  triatomae,  a  New  Flagellate  from  a  Hemipteran  Bug  from 

the  Nests  of  the  Wood  Rat  Neotoma  fuscipes,  by  Charles  Atwood  Kofoid 

and  Irene  McCulloch.    Pp.  113-126,  plates  14-15.    February,  1916 15 

11.  The  Genera'  Monocercomonas  and  Polymasti-x,  by  Olive  Swezy.    Pp.  127-138, 

plates  16-17.     February,  1916  10 

12.  Notes  on  the  Spiny  Lobster  (Panulirus  interruptus)  of  the  California  Coast, 

by  Bennet  M.  Allen.    Pp.  139-152,  2  figures  in  text.    March,  1916 15 

13.  Notes  on  the  Marine  Fishes  of  California,  by  Carl  L.  Hubbs.    Pp.  153-169, 

plates  18-20.    March,  1916 .15 

14.  The  Feeding  Habits  and  Food  of  Pelagic  Copepods  and  the  Question  of 

Nutrition  by  Organic  Substances  in  Solution  in  the  Water,  by  Calvin  O. 
Esterly.    Pp.  171-184,  2  figures  in  text.    March,  1916 ,15 

15.  The  Kinetonucleus  of  Flagellates  and  the  Binuclear  Theory  of  Hartmann, 

by  Olive  Swezy.    Pp.  185-240,  58  figures  in  text.    March,  1916 50 

16.  On  the  Life-History  of  a  Soil  Amoeba,  by  Charlie  Woodruff  Wilson.    Pp. 

241-292,  plates  18-23.    July,  1916  60 

17.  Distribution  of  Land  Vertebrates  of  Southeastern  Washington,  by  Lee 

Raymond  Dice.    Pp.  293-348,  plates  24  26.    June,  1916 60 

18.  The  Anatomy  of  Heptanchus  maculates:  the  Endoskeleton,  by  J.  Frank 

Daniel.    Pp.  349-370,  pis.  27-29,  8  text  figures.    December,  1916 25 

19.  Some  Phases  of  Spermato genesis  in  the  Mouse,  by  Harry  B.  Yocom.    Pp. 

371  380,  plate  30.    January,  1917  . 10 

20.  Specificity  in  Behavior  and  the  Relation  between  Habits  in  Nature  and 

Reactions  in  the  Laboratory,  by  Calvin  O.  Esterly.    Pp.  381-392.    March, 
1917  10 

21.  The  Occurrence  of  a  Rhythm  in  the  Geotropism  of  Two  Species  of  Plank- 

ton Copepods  when  Certain  Recurring  External  Conditions  are  Absent,  by 
Calvin  O.  Esterly.    Pp.  393-400.    March,  1917  .      .10 

22.  On  Some  New  Species  of  Aphroditidae  from  the  Coast  of  California,  by 

Christine  Essenberg.    Pp.  401-430,  plates  31-37.    March,  1917 .35 

23.  Notes  on  the  Natural  History  and  Behavior  of  JSmerita  analog  a  (Stimpson), 

by  Harold  Tupper  Mead.    Pp.  431-438,  1  text  figure.    April,  1917 10 

24.  Ascidians  of  the  Littoral  Zone  of  Southern  California,  by  William  E.  Ritter 

and  Ruth  A.  Forsyth.    Pp.  439-512,  plates  38-46.    August,  1917 1.00 

Vol.  17.   1.  Diagnoses  of  Seven  New  Mammals  from  East-Central  California,  by  Joseph 
Grinnell  and  Tracy  I.  Storer.    Pp.  1-8. 

2.  A  New  Bat  of  the  Genus  Myotis  from  the  High  Sierra  Nevada  of  Cali- 

fornia, by  Hilda  Wood  Grinnell.    Pp.  9-10. 

Nos.  1  and  2  in  one  cover.    August,  1916 10 

3.  Spelerpes   platycephalus,   a  New  Alpine   Salamander   from   the   Yosemite 

National  Park,  California,  by  Charles  Lewis  Camp.    Pp.  11-14.    Septem- 
ber, 1916  05 

4.  A  New  Spermophile  from  the  San  Joaquin  Valley,  California,  with  Notes 

on  Ammospermophilm  nelsoni  nelsoni  Merriam,  by  Walter  P.  Taylor.    Pp. 
15-20,  1  figure  in  text.    October,  1916  .05 

5.  Habits  and  Food  of  the  Roadrunner  in  California,  by  Harold  C.  Bryant. 

Pp.  21-58,  plates  1-4,  2  figures  in  text.    October,  1916 35 

6.  Description  of  Buf o  canorus,  a  New  Toad  from  the  Yosemite  National  Park, 

by  Charles  Lewis  Camp.    Pp.  59-62,  4  figures  in  text.    November,  1916 05 

7.  The  Subspecies  of  Sceloporus  occidentalis,  with  Description  of  a  New  Form 

from   the   Sierra   Nevada   and   Systematic   Notes   on    Other    California 
Lizards,  by  Charles  Lewis  Camp.    Pp.  63-74.    December,  1916 10 

8.  Osteological  Relationships  of  Three   Species  of  Beavers,  by  F.   Harvey 

Holden.    Pp.  75-114,  plates  5-12,  18  text  figures.    March,  1917 .40 

9.  Notes  on  the  Systematic  Status  of  the  Toads  and  Frogs  of  California,  by 

Charles  Lewis  Camp.    Pp.  115-125,  3  text  figures.    February,  1917 10 


UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS— (Continued) 

10.  A  Distributional  List  of  the  Amphibians  and  Reptiles  of  California,  by 

Joseph  Grinnell  and  Charles  Lewis  Camp.    Pp.  127-208,  14  figures  in  text. 
July,  1917  85 

11.  A  Study  of  the  Races  of  the  White-Fronted  Goose  (Anscr  albifrons)  Occur- 

ring in  California,  by  H.  S.  Swarth  and  Harold  C.  Bryant.    Pp.  209  222, 

2  figures  in  text,  plate  13.    October,  1917  15 

Vol.  18.   1.  Mitosis  in  Giardia  Microti,  by  William  C.  Boeck.    Pp.  1-26,  plate  1.    Octo- 
ber, 1917  35 

2.  An  Unusual  Extension  of  the  Distribution  of  the  Shipworm  in  San  Fran- 

cisco Bay,  California,  by  Albert  L.  Barrows.    Pp.  27-43.    December,  1917.      .20 

3.  Description  of  Some  New  Species  of  Polynoidae  from  the  Coast  of  Cali- 

fornia, by  Christine  Essenberg.    Pp.  45-60,  plates  23.    October,  1917 20 

4.  New  Species  of  Amphinomidae  from  the  Pacific  Coast,  by  Christine  Essen- 

berg.    Pp.  61-74,  plates  4-5.    October,  1917  15 

5.  Crithidia  Euryophthalmi,  sp.  nov.,  from  the  Hemipteran  Bug,  Euryophthalmus 

Convivus  Stal,  by  Irene  McCulloch.    Pp.  75-88,  35  text  figures.    Decem- 
ber, 1917  15 

6.  On  the  Orientation  of  Erythropsis,  by  Charles  Atwood  Kofoid  and  Olive 

Swezy.  Pp.  89-102,  12  figures  in  text.    December,  1917 15 

7.  The  Transmission  of  Nervous  Impulses  in  Relation  to  Locomotion  in  the 

Earthworm,  by  John  F.  Bovard.    Pp.  103-134,  14  figures  in  text.    January, 
1918    35 

8.  The  Function  of  the  Giant  Fibers  in  Earthworms,  by  John  F.  Bovard.    Pp. 

135-144,  1  figure  in  text.    January,  1918 10 

9.  A  Rapid  Method  for  the  Detection  of  Protozoan  Cysts  in  Mammalian 

Faeces,  by  William  C.  Boeck.    Pp.  145-149.    December,  1917 05 


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